The correlation between serum hepatitis C virus (HCV)-RNA and aminotransferase levels following completion of interferon therapy was evaluated in eight relapsed patients with chronic hepatitis C. Both HCV-RNA and aminotransferase levels were significantly increased in the relapsed patients 1 month after completion of therapy, compared to pretreatment values, despite aminotransferase levels being normal and HCV-RNA being undetectable by reverse transcription polymerase chain reaction assay at the end of therapy. The serum levels of HCV-RNA and aminotransferase were significantly elevated 1 and 2 months post-treatment. They then decreased to pretreatment values 3-5 months after the completion of therapy. Thus, in relapsed patients after the completion of therapy, the changes in HCV-RNA levels preceded the elevation in aminotransferase levels. These findings suggest a correlation between serum HCV-RNA levels and aminotransferase levels in relapsed patients with chronic hepatitis C after the completion of interferon therapy.