Hepatitis viruses and the acquired immunodeficiency viruses often infect intravenous drug addicts (IVDAs). Our study includes 255 IVDAs (26 females and 229 males, aged 20-35 years) from Cagliari. Of 255 subjects examined, 207 (81.1%) were positive for anti-HCV and 84 (32.9%) for anti-HIV. Nineteen (7.4%) subjects were HBsAg carriers, and 12 of these (63%) had an HDV superinfection. Markers of previous HBV infections were tested in 223 cases and 137 (61.4%) were found positive; of these 14 (10.2%) also had HDV infection. Of the 223 drug addicts examined for all infection markers, 18 (8%) were negative to all markers, 46 (20.6%) were positive to only one, 89 (39.9%) were positive to two, 64 (28.7%) to three and 6 (2.6%) were positive to all. Subjects with a single infection were significantly fewer than those with multiple infections. The correlations studied among the various markers did not point out any statistically significant associations. Even so, a previous HBV infection was more common while active HBV/HDV infections were less common among subjects with anti-HCV; HDV infection was more common among HIV-positive subjects. In HBsAg carriers neither HBV-DNA nor HCV-RNA was detected; HCV-RNA was found more frequently in anti-HIV positive subjects than in subjects with the anti-HCV isolate.