Between October 1984 and May 1986, 746 homosexual men, living in and around Amsterdam, The Netherlands, were surveyed at three consecutive six months periods regarding their sexual behavior. At the start of the study all subjects, of whom 234 (31 per cent) were HIV-Ab seropositive, were informed about their HIV antibody status. Seropositives initially reported more sexual partners than seronegatives; they also showed a greater reduction in the number of sexual partners and the number of partners with whom all forms of sexual practices were performed than did seronegatives. In both groups subjects were more likely to terminate orogenital intercourse than anogenital intercourse and masturbation.