The dynamics of alanine aminotransferase (ALT), anti-hepatitis C virus and hepatitis C virus (HCV) RNA in six cases with chronic HCV infection were studied for 3-7 years. Two of the six cases showed continued elevation of ALT, and three showed intermittent elevation. All cases were persistently positive for anti-HCV after initial seroconversion. Five of the six cases were persistently positive for HCV RNA detected by nested polymerase chain reaction, and one was positive intermittently. Thus hepatitis C virus replicates continually in a majority of patients with chronic hepatitis C, although some cases may show intermittent replication, and replication of hepatitis C virus does not always correlate with elevated ALT.