As part of the prospective AIDS study in Amsterdam, blood samples were collected from 741 heatthy homosexual men with multiple sexual partners, between October 1984 and May 1985. Samples were analyzed for the presence of antibodies to the human immunodeficiency virus (anti-HIV). Anti-HIV was demonstrated in 233 (31%) of the respondents. Seropositive respondents engaged in anal receptive sexual techniques with more sexual partners than did seronegative respondents, whereas seronegatives engaged in manual sexual techniques with more sexual partners than did seropositives. As far as it was possible to control for the interrelations between the measured variables, a direct relation with anti-H IV was established. This leads to the conclusion that when the number of sexual partners is considered a risk factor for HIV, a clear distinction should be made between the sexual techniques practiced with these partners. Two other risk factors for the presence of anti-HIV were the use of cannabis and of nitrite.