We studied the role of genital ulcerative infections for acquisition of human immunodeficiency virus type 1 (HIV-1) infection in a cohort of 989 homosexual men in Amsterdam between October 1984 and December 1988. Among 53 HIV-1 seroconverters serological and anamnestic data were gathered regarding herpes simplex virus type 2 (HSV-2) and syphilis in the 6 months before seroconversion. For statistical analysis a control who remained seronegative during the same interval was selected at random for each HIV-1 seroconverter. A significant difference between the prevalence of HSV-2 antibodies among HIV-1 seroconverters and controls was found (72% vs 38%). HSV-2 seroconversions among men initially seronegative for HSV-2 were found among three of 18 HIV-1 seroconverters and among three of 36 controls. (O.R. = 2.2, 95% C.I. 0.4-12.1). Self-reported cases of anogenital herpes were found more frequently among HIV-1 seroconverters (8) than among controls (4). One case of syphilis was diagnosed among HIV-1 seroconverters, and one among controls. Summing up these cases we assessed the total number of genital ulcerative infections: 12 among HIV-1 seroconverters and eight among controls (23 vs 15%, O.R. 1.7, C.I. 0.6-4.62). These data suggest little evidence for genital ulcerative infections being an important independent risk factor for HIV-1 acquisition among homosexual men in Amsterdam during the time period studied.