SummaryAnalyses of 24-hour specimens of urine from healthy adult males for androsterone and etiocholanolone produced values which, when calculated as discrinant scores, discriminated between heterosexual and exclusively homosexual individuals. This confirms a previous study.No significant differences were found between heterosexuals and homosexuals in parental ages, secondary sex characteristics, genitalia, anthropometry, 17-ketosteroids, and 17-ketogenic steroids.A significant difference was found between the heterosexual group and homosexual group in the number of homosexual relatives in the immediate and extended families. IntroductionIn the past few years the concept of a biological basis for homosexual behaviour has been reconsidered as a consequence of more precise investigative techniques. A previous study by Margolese (1970) showed that healthy adult males excreted androsterone and etiocholanolone in ratios that clearly discriminated between heterosexual and homosexual subjects. This was followed by a study by Lorraine (1970) who found low urinary testosterone in two homosexual males and raised urinary itestosterone in four homosexual females. The idea that changes in endocrine function might contribute to the genesis of homosexuality in humans was then given further impetus by Kolodny et al. (1971) who showed that plasma testosterone levels of a homosexual group were significantly lower than those of a control group. When investiga-ting several biochemical parameters Evans (1972) found that homosexuals had a lower androsterone/