HENNESSEY, C.J.

We have before us a broad scale attack on the Massachusetts law against prostitution. The defendants, Rebecca Jones, Barbara Astrofsky, and Diane King, all were convicted for violations of G.L.c. 272, § 53. Jones and Astrofsky were convicted in a Municipal Court, appealed, and then were tried and convicted by a judge in the Superior Court on complaints of prostitution. King, after appealing her Municipal Court convictions, was tried and convicted by judges in the Superior Court on three complaints of prostitution and two complaints of common night walking, all pursuant to § 53. Fines and thirty-day suspended sentences, with periods of probation, were imposed in all cases except one case against King, wherein a six-month sentence was imposed.

In each of the seven cases below, before conviction in the Superior Court, the defendant filed motions to dismiss the complaint and for the entry of a finding of not guilty on the complaint, alleging that c. 272, § 53, is unconstitutional on its face and as applied to the defendant in that case. The judge in each case denied both motions, and the defendant in each case took exceptions to the denial of her motions. Because the motions and exceptions in all the cases raise common issues, the defendants consolidated their cases for the purposes of appeal. This court took jurisdiction of the consolidated appeal which is before us on bills of exceptions. Execution of the defendants' sentences was stayed pending appeal. We find no error and overrule the exceptions in all cases.

The facts underlying each conviction can be summarized as follows.

Jones.

In July, 1975, Officer McNelley of the Boston police department telephoned Jones, informing her that he had obtained her name from a male friend. When she said she could not remember this person, they arranged an appointment for the same afternoon. At that meeting, Jones informed Officer McNelley that she would perform various sexual acts with him for $50. He then arrested her and filed a complaint that "Rebecca Jones . . ., a female, was a prostitute offering her body to indiscriminate intercourse with men for hire." Officer McNelley testified that he has never brought a similar complaint against a man and that it is the practice of the vice squad division of the Boston police department to file such complaints against only females.

Astrofsky.

In November, 1975, Officer Flemming of the Boston police department observed Astrofsky with another woman in a hotel bar being approached by men. He engaged them in conversation. According to his testimony, her companion asked him, in Astrofsky's absence, whether he "was interested in going out for $75.00 each." She informed Astrofsky of his interest in "going out" for this price, and Astrofsky volunteered the information that fellatio and sexual intercourse would be included. Officer Flemming then arrested both women. He filed a complaint that "Barbara Astrofsky . . . [b]eing a female, was a prostitute offering her body to indiscriminate intercourse with men for hire."

King — Cases 1, 2 and 3 (prostitution).

In April, 1975, according to the testimony of Officer Milan of the vice control unit of the Boston police department, he observed King conversing with the operator of a motor vehicle. She entered the car; it drove away. Then he and a fellow officer stopped the car. The operator of the car informed the officers that King had solicited him for sexual intercourse for $20 and that the act was to take place in his car. Thereupon the officers arrested King and filed a complaint that "Diane King . . ., being a female, was a prostitute offering her body to indiscriminate intercourse with men for hire." The record does not show whether the officers also arrested the operator of the car.

In May, 1975, Detective DeLuca of the Boston police department was approached by one Debbie Wilson, who offered to engage in fellatio and sexual intercourse for $25. After he agreed to Wilson's terms, King approached the couple and offered, for an additional $25, to join Wilson in performing sexual acts with Detective DeLuca. He then arrested both women and filed a complaint that "Diane King . . ., being a female, was a prostitute offering her body to indiscriminate intercourse with men for hire."

In July, 1975, Detective McCormick of the Boston police department observed King getting into a car, followed the car, and stopped it. The male occupant of the car informed Detective McCormick that King had offered to perform sexual intercourse with him for $25, and that they were en route to her apartment. Detective McCormick then arrested King and filed a complaint charging her with prostitution in language identical to Detective DeLuca's. The record does not show whether Detective McCormick also arrested the male occupant of the car.

King — Cases 4 and 5 (common night walking).

On July 13, 1975, at approximately 11:30 P.M. Patrolman Fee of the Boston police department observed King on a Boston street corner approaching and conversing with males who were on foot and in cars. He ordered her to stop this activity and she complied. On two subsequent nights he observed King engaging in similar activity. On the first such occasion he ordered her to leave the area. On the second such occasion he arrested her and filed a complaint that "Dianne [ sic] King . . . was and now is a common night walker." After this arrest, Patrolman Fee in King's presence conversed with an unidentified male who informed him that King had asked whether he wanted to go out and whether he could spend $20.

On June 9, 1975, at 3 A.M. Detective Powers of the Boston police department observed King on a Boston street corner approaching cars with male occupants. He warned her to leave the area and she complied. On June 21, 1975, at 3:55 A.M. Detective Powers observed King entering a car, stopped the car and told her to leave the area. At 4:35 A.M. he observed her at the same location, entering a car. He followed the car to Atlantic Avenue in Boston, where the driver parked the car. Detective Powers arrested King, charging her with common night walking in language identical to Patrolman Fee's.

1. The defendants assert that G.L.c. 272, § 53, in so far as it prohibits prostitution is facially unconstitutional because its definition of proscribed conduct is vague; because it prohibits the status of being a prostitute; because it discriminates against women; and because the statute proscribes conduct which is protected by the right of privacy. In addition, they argue that the § 53 proscription of prostitution was unconstitutionally applied in each of the five cases below because § 53 is enforced against female prostitutes but not against male prostitutes; because § 53 is enforced against female prostitutes but not against their male customers; because the Commonwealth failed to prove the necessary elements of the offense of prostitution in these cases; and because application of § 53 in these cases invaded the defendant's rights to privacy. Finally, the defendants maintain that § 53, in so far as it prohibits common night walking, is unconstitutionally vague as applied to King.

We hold that the prostitution provision of G.L.c. 272, § 53, as construed in this opinion, is not facially unconstitutional. In addition, we hold that the records do not show unconstitutional application of that provision to the defendants. We also hold that the common night walking provision of § 53 was not unconstitutionally vague in its application to King. Finally, we hold that the Commonwealth here proved the essential elements of the charge of prostitution, since proof of solicitation by the defendants for such acts is sufficient.

2. CONSTITUTIONALITY — DUE PROCESS — VAGUENESS.

The defendants contend that the terms "prostitutes" and "common night walkers" in § 53 are so vague as to violate the constitutional principle of due process of law in that these terms fail to give sufficient warning and definition of the proscribed conduct.

Prostitutes.

General Laws c. 272, § 53, provides in pertinent part: "[P]rostitutes . . . may be punished by imprisonment in a jail or house of correction for not more than six months, or by a fine of not more than two hundred dollars, or by both such fine and imprisonment." In 1959, the Legislature inserted the term "prostitutes" into the list of criminal offenses contained in § 53 without specifically defining the persons who may be punished as "prostitutes" under § 53. St. 1959, c. 304, § 1. At the same time the Legislature inserted into the list of permissible forms of complaints and indictments contained in G.L.c. 277, § 79, a form for the § 53 crime of prostitution which reads "[t]hat A.B. a female, was a prostitute offering her body to indiscriminate intercourse with men for hire." St. 1959, c. 304, § 2.

The defendants argue that the Legislature's failure to define the conduct proscribed in its 1959 amendment to § 53 renders that provision unconstitutionally vague because potential defendants have insufficient warning of the criminality of their conduct. Cf. Commonwealth v. A Juvenile, 368 Mass. 580, 586 (1975). We do not agree.

Although no crime of prostitution by that name exists at common law ( Commonwealth v. Cook, 12 Met. 93, 97 [1846]), it can also be said that the Legislature did not create or define a new crime, "prostitution," by enacting St. 1959, c. 304, § 1. General Laws c. 272, § 53, does not create or define new crimes, but rather prescribes penalties for the commission of acts previously recognized as criminal offenses. Commonwealth v. Brasher, 359 Mass. 550, 554 (1971). The statute drew together for reclassification purposes criminal acts of the same essential nature (commercial sex) so that law enforcement officials could focus efficiently on this type of criminal conduct. These reclassified acts had been proscribed for more than 250 years by the statute punishing "lewd, wanton and lascivious persons in speech or behavior." See, e.g., Province Laws 1699-1700, c. 8, § 2; G.L.c. 272, § 53, as amended; G.L.c. (Ter. Ed.) c. 272, § 53, as amended; Commonwealth v. Diamond, 248 Mass. 511, 517 (1924) (solicitation to and performance of lewd acts for money constitute being a lewd, wanton, and lascivious person in speech or behavior).

Since the Legislature failed to define the lewd, wanton, and lascivious speech and behavior it reclassified as prostitution, we turn to common understanding for definition of the conduct reclassified in St. 1959, c. 304, § 1. See Thomes v. Commonwealth, 355 Mass. 203, 207 (1969); Alegata v. Commonwealth, 353 Mass. 287, 304 (1967).

That understanding, as clearly stated by this court in construing other statutes, is that a prostitute is one who permits common indiscriminate sexual activity for hire, in distinction from sexual activity confined exclusively to one person. See Commonwealth v. Cook, 12 Met. 93, 97 (1846); Commonwealth v. Harrington, 3 Pick. 26 (1825). We conclude that that is the conduct intended to be punished by § 53.

Thus defined, § 53 is not vague. Moreover, this definition includes conduct which persons of ordinary understanding would classify as prostitution. As the defendants themselves point out, conduct known as prostitution has existed since time immemorial. This conduct traditionally has included both performance of sexual acts as a business and public solicitation for such business. See Cook, supra at 97. The conduct for which the defendants were convicted as prostitutes falls squarely within this traditional understanding of the terms "prostitute" and "prostitution." Therefore they cannot successfully maintain that the prostitution provision of § 53 is unconstitutionally vague on its face without judicial clarification of the conduct it punishes. See Commonwealth v. Orlando, 371 Mass. 732, 734 (1977); Coates v. Cincinnati, 402 U.S. 611, 614 (1971).

Common Night Walkers.

The defendants maintain that King's convictions of common night walking pursuant to G.L.c. 272, § 53, violate the due process provisions of the United States Constitution and the Massachusetts Constitution, by reason of the vagueness of the statutory language. This court has construed the common night walking provision of § 53 as punishing persons abroad at night who solicit others to illicit sexual acts. Thomes v. Commonwealth, 355 Mass. 203, 206-207 (1969). We held in Thomes that, as thus construed, the common night walker provision of § 53 is not unduly vague. We now reaffirm that holding.

King was convicted twice of common night walking on evidence in each case that police officers observed her on numerous occasions late at night, within the space of several weeks, in the same general vicinity, approaching and conversing with men. The arrest in each case occurred after she had on earlier occasions been ordered to leave the area. We conclude that this evidence was sufficient to sustain her convictions of common night walking. The time, place, and frequency of King's conduct warrant an inference that on each occasion observed by the police King was soliciting men for illicit sexual intercourse. Section 53 is not a statute directed against recidivism and does not require proof of past convictions for prostitution to sustain a conviction for common night walking.

3. CONSTITUTIONALITY — RIGHT OF PRIVACY.

Our definition of prostitution comprises two grounds for conviction under § 53: performance of indiscriminate sexual acts for hire and indiscriminate solicitation or agreement to perform sexual acts for hire. The defendants' convictions for prostitution clearly rested on the latter ground. Evidence at trial indicated that, while in a place to which the public had access, the defendants either offered or agreed to perform various sexual acts with other persons in exchange for money. Therefore, their convictions, relying on no private conduct, implicate no constitutionally protected rights of privacy. Although a conviction for prostitution based on performance of sexual acts for hire conceivably could rely on conduct performed in private, we do not decide whether such a conviction would implicate a right of privacy. Defendants may not properly base their claim that § 53 is facially unconstitutionally on its possible unconstitutionality as applied to others. Commonwealth v. Balthazar, 366 Mass. 298, 302 (1974). Commonwealth v. LaBella, 364 Mass. 550, 553-554 (1974).

4. CONSTITUTIONALITY — EQUAL PROTECTION OF THE LAWS.

The defendants raise the constitutional issue of equal protection of the laws in three aspects. The first two of these aspects go to the alleged facial unconstitutionality of § 53 in that that statute assertedly provides for punishment of female prostitutes but not male prostitutes, and also makes no provision for punishment of the hirer or customer of the prostitute. The third argument is that the statute was unconstitutionally applied against these defendants by reason of discriminatory enforcement of law.

Male and Female Prostitutes.

Prostitution as defined in this opinion comprises conduct of all persons, male and female, who engage in sexual activity as a business. Thus, G.L.c. 272, § 53, as construed, applies to male prostitutes as well as to female prostitutes. It is argued by the defendants that a contrary construction of § 53 would violate the equal protection provisions of the Massachusetts Constitution as well as the recent amendment thereto which expressly provides that equality under the law shall not be denied on the basis of sex. Where possible, we construe statutes in such a way that they are constitutional. Alegata v. Commonwealth, 353 Mass. 287, 290 (1967). The definition of prostitution herein adopted avoids any possibility of unnecessary unconstitutionality. In light of our construction of the statute, we need not consider the further argument of the Commonwealth that, even if the prostitution provision were held to apply only to women, it would not be considered discriminatory since there are other crimes which in essence charge males with the same offense under different wording: e.g., unnatural and lascivious acts under G.L.c. 272, § 35, and the common law crime of soliciting for an unnatural act.

The "Hirer" or "Customer."

The definition of prostitution set forth, supra, does not include the conduct of persons who hire or seek to hire another to engage in sexual activity. Nonetheless we do not agree with the defendants' argument that such a definition of prostitution unconstitutionally criminalizes female conduct but not male conduct.

We note at the outset that the person challenging the constitutionality of a legislative enactment has an onerous burden of proof in establishing the invalidity of the statute. Commonwealth v. Chamberlain, 343 Mass. 49, 51 (1961). This court will afford a presumption of constitutionality to the statute, which means that all rational inferences are made in favor of the legislation. Commonwealth v. Henry's Drywall Co., 366 Mass. 539, 541 (1974).

Applying these principles to § 53, in the face of a claim that it violates the defendants' constitutional right to equal protection of the laws, we may properly consider that § 53 was designed to attack merely one phase of a problem. "The legislature may select one phase of one field and apply a remedy there, neglecting the others." Williamson v. Lee Optical of Okla., Inc., 348 U.S. 483, 489 (1955). In somewhat analogous statutes, the Legislature has provided criminal penalties for the provider or seller, and not the customer or buyer, of obscene materials (G.L.c. 272, §§ 28, 29) and for the seller of goods, and not the buyer, in cases where the "Sunday law" is violated. G.L.c. 136, § 5.

In light of our conclusions, we need not consider the further argument that might be offered by the Commonwealth that a correlative crime, "lewd, wanton and lascivious . . . speech or behavior," is also provided in § 53; that this crime may apply to those who purchase and attempt to purchase sexual acts, and that thus the statute covers all participants in the business of sex for hire without regard to their status as seller or buyer. See Commonwealth v. O'Brien, 179 Mass. 533 (1901).

Discriminatory Enforcement.

The defendants argue that the prostitution provision of G.L.c. 272, § 53, even if facially constitutional, is unconstitutional as applied to each of the seven cases involved in this appeal. They aver that the Commonwealth selectively enforces § 53 on the basis of sex, in violation of the equal protection provisions of the United States Constitution and the Massachusetts Constitution.

The defendants allege that there existed at the times of their arrests law enforcement policies and practices whereby female prostitutes were prosecuted under § 53 while male prostitutes and male customers of prostitutes were not. In so far as their claim is that of sex-based practices in the failure of authorities to prosecute male customers of prostitutes, their contention fails because they presented no evidence to show that their customers were not arrested and prosecuted. As to this issue, the record is left conjectural. Further, it is the opinion of a majority of the court (see the separate opinion of Hennessey, C.J., post) that, to the extent that the defendants rely on the failure to arrest and prosecute customers, what we have said supra, concerning the legislative privilege to criminalize the conduct of the prostitute and not the customer, is dispositive. It cannot be fairly argued that there is discriminatory enforcement when there is no statutory provision for the prosecution of the customers.

In so far as the defendants King and Astrofsky alleged unlawful discrimination in the consistent failure of police to prosecute male prostitutes their argument fails because they presented no supporting evidence in the trial court. They included in their appellate briefs statistical evidence which would tend to be supportive. However, we can decide cases only on the records before us, so this evidence is not properly to be considered. Such evidence should have been presented at the trial level together with the defendants' motions to dismiss their complaints because of unequal application of § 53 on the basis of sex. Consequently, we find on the records before us that any inference of sex-based practices in the enforcement of § 53, as applied to King and Astrofsky, can rest only on conjecture. The motions to dismiss their complaints were properly denied.

The defendant Jones, unlike King and Astrofsky, attempted to prove discrimination by the presentation of evidence. Thus, at the trial of Jones, the arresting officer testified that he had never arrested a male prostitute and that it was the policy of the Boston police department vice squad to arrest only female prostitutes.

It is argued that, although Officer McNelley does not speak for the police department, it should be inferred from his evidence that the Boston police department follows a practice of enforcing the prostitution provision of § 53 only against women. Even if that premise is accepted, however, it falls far short of establishing any evidence of a denial of equal protection since other criminal statutes may be employed to punish male conduct equivalent to female prostitution. State v. Price, 237 N.W.2d 813, 815 (Iowa 1976). It is left entirely conjectural in the record before us whether males who solicited for or engaged in sexual relations for hire, but were not arrested for prostitution, were charged instead with any number of other applicable criminal offenses including: common night walking under G.L.c. 272, § 53; the common law crime of soliciting for an unnatural act, see Commonwealth v. Scagliotti, 373 Mass. 626 (1977); sodomy under G.L.c. 272, § 34; and unnatural and lascivious acts under G.L.c. 272, § 35. It is clear that Jones's motion to dismiss the complaint against her was rightly denied.

The "Equal Rights" Amendment.

What we have said thus far leads us to conclude that we shall affirm the judgments in all cases. In doing so we have established that the statutory provisions of G.L.c. 272, § 53, relevant to these cases are facially constitutional. We have also held that the defendants fail, by reason of our present statutory framework, to prove sex-based discrimination in the alleged failure to prosecute customers as well as prostitutes. However, in disposing of the defendants' further contention that the statute was unconstitutionally and discriminatorily applied against women by reason of the police failure to prosecute male prostitutes, we concluded only that the record before us clearly does not raise a sufficient factual basis to support that argument. Thus, we believe that further comment is desirable as to this aspect of the case.

We conclude that a female charged with prostitution or night walking would be entitled to a dismissal of the charges with prejudice on an appropriate showing that the police department or the prosecutor's office followed an unjustifiable policy of selective enforcement against female prostitutes and not male prostitutes.

It is important to note at the outset that there is a considerable area of discretion in prosecutors which permits the exercise of some selectivity for valid reasons consistent with the public interest (e.g., prosecution is forgone in the interest of gaining a cooperative witness). We have no intention of suggesting a narrowing of that area of valid prosecutorial discretion.

It is well established that the Fourteenth Amendment to the United States Constitution does not permit unequal application of impartial laws, Yick Wo v. Hopkins, 118 U.S. 356, 373-374 (1886), but does permit the "conscious exercise of some selectivity" in criminal law enforcement as long as the selectivity is not based on "an unjustifiable standard such as race, religion, or other arbitrary classification." Oyler v. Boles, 368 U.S. 448, 456 (1962). Following these principles, courts have reversed criminal convictions and dismissed criminal complaints as violative of equal protection principles when they found selectivity in prosecution based on impermissible standards. See, e.g., United States v. Falk, 479 F.2d 616 (7th Cir. 1973) (selective enforcement of failure to possess a selective service registration card law against vocal draft resisters based on exercise of right of free speech); United States v. Steele, 461 F.2d 1148 (9th Cir. 1972) (selective enforcement of census form statute against census resisters who exercised right of free speech); United States v. Crowthers, 456 F.2d 1074 (4th Cir. 1972) (selective enforcement of Federal regulations concerning disturbance against war resisters on the basis of political opinions); United States v. Robinson, 311 F. Supp. 1063 (W.D. Mo. 1969) (selective enforcement of wiretap law against private offenders but not against governmental offenders); People v. Acme Mkts. Inc., 37 N.Y.2d 326 (1975) (selective enforcement of Sunday sales law against stores only on labor union complaints).

The Massachusetts Constitution, as it existed at the time of the defendants' trials, did not permit the Commonwealth to make distinctions based on sex unless the distinctions bore a fair and substantial relationship to a permissible State objective. Commonwealth v. MacKenzie, 368 Mass. 613, 615-616 (1975). This equal protection standard applies to the cases at hand. However, in 1976 the people of Massachusetts amended art. 1 of their Constitution, declaring that "[e]quality under the law shall not be denied or abridged because of sex, race, color, creed or national origin." See art. 106 of the Amendments to the Constitution of the Commonwealth. Since the standards which derive from this amendment currently apply to cases involving sex-based classification, we herein elaborate those standards.

The classifications set forth in art. 106, supra, with the exception of sex, are within the extensive protection of the Fourteenth Amendment to the United States Constitution and are subjected to the strictest judicial scrutiny. See, e.g., Loving v. Virginia, 388 U.S. 1 (1967) (race as a suspect classification); Graham v. Richardson, 403 U.S. 365 (1971) (alienage as a suspect classification); Oyama v. California, 332 U.S. 633 (1948) (national origin as a suspect classification); Wisconsin v. Yoder, 406 U.S. 205, 214 (1972) (religious distinction affecting fundamental First Amendment rights). These classifications are permissible only if they further a demonstrably compelling interest and limit their impact as narrowly as possible consistent with their legitimate purpose. See, e.g., Commonwealth v. Henry's Drywall Co., 366 Mass. 539, 542 (1974); In re Griffiths, 413 U.S. 717, 721-722 (1973).

Article 106 incorporates into our State Constitution an express prohibition of discrimination on the basis of sex, grouping it with other prohibited bases for discrimination which are subject to strict judicial scrutiny. All the categorical bases listed therein logically are subject to the same degree of judicial scrutiny, and in our opinion that degree of scrutiny must be at least as strict as the scrutiny required by the Fourteenth Amendment for racial classifications. Therefore, we conclude that the people of Massachusetts view sex discrimination with the same vigorous disapproval as they view racial, ethnic, and religious discrimination.

Consequently, the Commonwealth cannot enforce G.L.c. 272, § 53, against female prostitutes but not against male prostitutes unless it can demonstrate a compelling interest which requires such a policy.

The defendant bears the initial burden of alleging and showing, prima facie, selective enforcement of the law on the basis of sex, because we presume that criminal arrests and prosecutions are undertaken in good faith, without intent to discriminate. See Manning v. Municipal Court of the Roxbury Dist., 372 Mass. 315 (1977); Falk, supra at 620. Law enforcement officials necessarily have wide discretion in determining whether to prosecute. 372 Mass. at 317. A defendant can meet this burden by presenting to the court, on a motion to dismiss, evidence which strongly suggests or raises a reasonable inference that there existed in connection with her arrest or prosecution a sex-based distinction in law enforcement practice in the consistent and unjustified failure to prosecute male prostitutes. See Falk, supra at 622-623; United States v. Crowthers, 456 F.2d 1074 (4th Cir. 1972); United States v. Robinson, 311 F. Supp. 1063, 1064 (W.D. Mo. 1969). Cf. Commonwealth v. Antobenedetto, 366 Mass. 51, 57 (1974) (defendant having shown that evidence was seized pursuant to allegedly unjustifiable search, prosecution has burden of establishing reasonableness of search).

Once a defendant has raised a reasonable inference that sex-based law enforcement practices are implicated in her arrest or prosecution, the Commonwealth must rebut that inference or suffer the underlying complaint to be dismissed.

5. CONCLUSION.

In summary, we find no error in King's convictions for prostitution and common night walking, and we find no error in the convictions of Astrofsky and Jones for prostitution.

Exceptions overruled.