Fifteen kidney transplant recipients with chronic hepatitis C were given 3 million units recombinant alpha2b-interferon for 142+/-35 days. There were significant decreases in hepatitis C virus (HCV) RNA 1 month after the initiation of treatment (p < 0.01), and at the end of treatment (p < 0.05). HCV RNA was undetectable by PCR analysis during treatment in 5 patients. But HCV RNA reappeared in all patients 1 month after the cessation of therapy, and the level of viremia returned to baseline. While all patients had normalized alanine aminotransferase (ALT) activities at the end of therapy, 11 experienced a relapse during the follow-up period (1 year). There was a correlation between the amount of HCV RNA at the end of treatment and the time of relapse. Serum IgM against core protein of HCV were detected in 7/15 patients. Anti-core IgM remained detectable during treatment and afterwards. There was no correlation between IgM status and other virological parameters, or ALT activity.