Chronic hepatitis B viral infection is common in human immunodeficiency virus (HIV) carriers, but the effectiveness of interferon therapy is still unknown. We report the results of a long-term pilot study of five patients, who were infected with HIV and chronic hepatitis B, treated by interferon. Five males co-infected with HIV and hepatitis B virus (HBV) (mean age 27 years) were given a 6-month course of interferon (IFN)-alpha 2b 5 million units (MU) three times weekly. On initiating the treatment, their CD4 lymphocyte count was 340-553 mm-3, their CDC stage was IIa-III; all had histologically proven chronic hepatitis, with Knodell's score ranging from 6-10, and active HBV replication (HBV DNA and hepatitis B e antigen (HBeAg) were detectable). There was no associated hepatitis delta virus (H delta V) or hepatitis C virus (HCV) infection. Follow-up was for 53 months on average (24-74 months). After the treatment, hepatitis B e antibody (HBeAb) and hepatitis B s antibody (HBsAb) seroconversion was observed in one patient, HBeAb seroconversion alone in two patients, HBV DNA was absent from serum in three patients, and HBV DNA significantly decreased in one patient. The serum alanine aminotransferase (ALT) activity was normal in four patients. Histological improvement was obtained in four patients. The HIV stage remained unchanged in all patients during the whole follow-up. These preliminary results suggest that interferon can be successfully used in immunocompetent HIV carriers with chronic hepatitis B as well as in HIV-negative patients.