We determine the correlation between viremia in serum specimens, transaminase activity (ALT and AST) and histological grading in 37 patients with chronic hepatitis C. In addition we compared two PCR methods for hepatitis C virus (HCV)-RNA in serum specimens. For the histological grading we used a modified Knodell score. For detection and quantification we measured the viremia (HCV-RNA titer) with a standardized "nested primer" PCR (end-point dilution method) and the commercially available Amplicor HCV Monitor. The mean HCV-RNA and AST level was significantly higher in patients with a histologically active inflammation. In the individual patient we could not conclude from the titer of HCV-RNA on the histologic grading because of the wide range of the results. We did not find a significant difference in ALT in patients having varying histological gradings. HCV-RNA titer and transaminases (ALT and AST) did not correlate significantly. The HCV-RNA titer was significantly marked in older patients (above 40 years) and patients having sporadic hepatitis than in younger patients and patients with chronic hepatitis after drug abuse. The "nested primer" PCR (end-point dilution method) was more sensitive for detection of HCV-RNA in serum specimens than Amplicor HCV Monitor. The lack of HCV-RNA with Amplicor HCV Monitor in 12 of 37 patients (32%) did not rule out viremia. We conclude that in patients with a chronic hepatitis C marked viremia points to a histologically active inflammation. In the individual patient we could not conclude from the titer of HCV-RNA on the histological grading. Because of the lower sensitivity of Amplicor HCV Monitor it is necessary to confirm negative results with a "nested primer" PCR.