Information is scarce on the prevalence of hepatitis B (HBV) and hepatitis C (HCV) among voluntary blood donors and patients infected with the human immunodeficiency virus (HIV) in Florianópolis, Brazil. A total of 2,678 serum samples from 2,583 blood donors and 95 HIV-infected patients, collected between April, 1994, and March, 1995, were examined for markers of HBV and HCV. All the samples were analyzed to detect HBV and HCV markers (HBsAg, anti-HBc, and anti-HCV). Hepatitis B and C prevalence among the studied blood donors reached 9.3% and 1.0%, respectively; 0.7% being seropositive for HBsAg and 9.2% for anti-HBc. It was also verified that 0.1% of blood donors were seropositive for HBsAg alone, 8.6% seropositive for the anti-HBc alone, and 0.6% presented a positive reaction for both of the HBV markers studied. Among HIV-infected patients, prevalence of 69.5% and 54.7% for hepatitis B and hepatitis C, respectively, were observed. Of these patients, 18.9% were seropositive for HBsAg, and 66.3% for the anti-HBc. The prevalence of a reaction for HBsAg alone, and for anti-HBc alone was 3.1% and 50.5%, respectively, for HIV-infected patients, whereas 15.8% were seropositive for both of the studied markers. HBV and HCV coinfection was 0.1% in blood donors, and 40% of those patients tested seropositive for HIV. Results show prevalence of HBV and HCV infection to be significantly greater among HIV-infected patients than among blood donors. These observations confirm the high frequency of HIV-infected patients exposure to these other viruses.