Fifty-seven male prostitutes who were also drug users, underwent HIV-1 testing in a drug dependency unit in Rome. The overall prevalence of HIV antibody was 74% (42/57). Of the 57 subjects, 46 completed a standard questionnaire and were interviewed by a trained psychologist about use of drugs, sexual and AIDS-related behaviours. Among the 46 patients responding to the questionnaire, the prevalence of HIV was 67% (31/46). HIV prevalence increased with the duration of drug use, rising from 48% for less than 2 years use, to 64% for 2 to 4 years, and 100% for more than 4 years. It also increased with duration of stay in Italy: from 59% for less than 2 years, 78% for 2-4 years and to 83% for more than 4 years. Prevalence of HIV antibody was higher among those who reported injecting drugs (73% vs 63%), or who reported needle sharing (83% vs 62%). Higher prevalence was also related to the number of partners in the last year (74% for more than 1,500 partners vs 50% for less than 1,500), and to non-use of condoms (70% for 'sometimes/never' vs 50% for 'always'). The results indicate that further educational outreach efforts are required among male transvestite prostitutes since they may constitute a potential source of infection for their clients.