In a homosexual communication centre in Antwerp 196 homosexual men were screened for seromarkers of syphilis, hepatitis A (HAV), hepatitis B (HBV) and cytomegalovirus (CMV). A comparison group consisted of 118 heterosexual men attending a venereal disease clinic in Antwerp. Treponemal antibodies were found in 7.1% of homosexual men, of whom half gave no history of past or present infection. Anti HAV was present in 43.3%, HBV seromarkers in 34.4%, and CMV antibodies in 71.2% of homosexual men. Hepatitis B surface antigen (HBsAg) was detected in eight homosexual men, but not in the heterosexual control group. Prevalence rates of infections other than HAV were significantly higher in homosexual men than in heterosexual men. Answers to a questionnaire were used to evaluate risk factors for different diseases, which were: duration of active homosexuality for all infections, promiscuity (greater than or equal to 10 partners in the past six months) for syphilis and hepatitis B, and anal intercourse for hepatitis B. Visiting saunas and travelling for sexual contacts also indicated a higher risk for STD, but were an indirect expression of promiscuity.