Hepatitis C virus genotype and the amounts of circulating HCV RNA are the most important factors in determining the efficacy of interferon therapy for chronic hepatitis C. To clarify the correlation of these two factors to the progression of liver disease, we classified 148 Japanese patients with type C chronic liver disease into genotypes and also measured their HCV RNA titers (logarithmic transformed copy number/ml serum) by competitive reverse transcription-polymerase chain reaction. We found type II in 23 (76.7%) of 30 patients with chronic persistent hepatitis, 34 (79.1%) of 43 with chronic active hepatitis, 29 (72.5%) of 40 with cirrhosis and 30 (85.7%) of 35 with hepatocellular carcinoma. Thus, there was no significant difference in the prevalence of type II among the various stages of chronic liver disease. We also found the RNA titer to be significantly higher in patients with chronic active hepatitis (8.0 +/- 0.8) than in those with chronic persistent hepatitis (7.0 +/- 1.0, p < 0.001), and also those with cirrhosis (7.6 +/- 0.8, p < 0.05) or hepatocellular carcinoma (7.7 +/- 0.8, p < 0.05). When the titers were compared among genotypes, there was no significant difference between type II and III at any stage (type II vs. type III: chronic persistent hepatitis, 7.2 +/- 1.0 vs. 6.7 +/- 0.8; chronic active hepatitis, 8.1 +/- 0.7 vs. 7.8 +/- 1.0; cirrhosis, 7.7 +/- 0.8 vs. 7.8 +/- 0.7; hepatocellular carcinoma, 7.7 +/- 0.8 vs. 7.8 +/- 0.5). In conclusion, although genotype affects interferon therapy efficacy, it seems to have little influence on serum RNA levels and the progression of type C chronic liver disease.