For identification of risk factors for progression of human immunodeficiency virus (HIV) infection, 746 homosexual men participating in a cohort study in Amsterdam, The Netherlands, were studied since October 1984. A total of 234 of these men were HIV antibody-positive at baseline, and 52 seroconverted during follow-up. These 286 individuals were categorized as high- and low-risk for progression to the acquired immunodeficiency syndrome (AIDS) on the basis of the presence or absence of HIV antigenemia, antibody to HIV core antigen, or a number of T helper lymphocytes less than 0.5 x 10(9)/liter during three or more subsequential blood samples. Ninety-six (41%) of the seropositives and 32 (62%) of those who seroconverted remained low-risk throughout the study period. Bivariate analyses revealed that educational level and a history of herpes zoster were associated with a low- and high-risk status, respectively. In multivariate analyses, a history of herpes zoster and a history of sexual intercourse with a person who had AIDS were associated with a more rapid disease progression. While herpes zoster is considered to be a marker of progressive immunodeficiency, a history of having sexual intercourse with a person who had AIDS points to the more virulent properties of HIV in these persons. Because both seropositives and seroconverters who had sexual intercourse with a person with AIDS had a more rapid disease progression, it seems plausible that being infected by a person with AIDS is a risk factor for a relative short incubation period.