Prevalence and determinants of HIV infection were assessed in 127 homosexual and bisexual men in the northeastern part of Italy. The overall prevalence of HIV seropositivity was still rather low: 20% (95% confidence interval -CI- 13-27%). The most important risk factor for acquiring HIV infection turned out to be having has sexual intercourses in high-risk areas. Relative risks (RRs) for those who have travelled and had sex in North Europe and in the U.S., were, respectively, 2.7 (95% CI: 1.0-7.3) and 5.6 (95% CI: 1.2-25.9). A significantly increased risk was also seen for having a steady sexual partner (RR = 3.1, 95% CI: 1.3-7.5). Use of nitrite inhalants, high number of occasional sexual partners and habitual receptive anal intercourses were also associated with elevation of risk, whereas prostitution was not. The present study confirms the patterns of HIV spread among homosexual and bisexual men from high-risk areas to low-risk areas and prompts urgent educational intervention, in order to prevent the epidemics of AIDS among Italian homosexuals from reaching the size documented in other countries.