A series of 320 German i.v. drug abusers (32.2% female, 67.8% male) were tested in a cross-sectional study for antibodies against HIV. Seroprevalence increased from 0 in those who discontinued i.v. drug abuse before 1982 to 37.2% in those who stopped injecting drugs in 1985/1986 or who were still addicted. Antibodies to HIV were significantly associated with lymphadenopathy and clinical symptoms (fever, weight loss, diarrhea, fatigue, night sweat, dermal lesions) and with markers of hepatitis A and hepatitis B virus infection. Participants of the study admitted in 92.5% of cases to "needle sharing" and in 83.1% of cases to sexual contacts among drug abusers. Prostitution and drug abuse in prison were significantly correlated with seropositivity. No antibodies to HIV infection were detected in 131 subjects of a control group of household contacts.