Abstract:To determine whether pretreatment HCV‐RNA level, hepatitis C virus genotypes, alanine aminotransferase and histology correlate with subsequent response to interferon‐α therapy or not, serum HCV‐RNA levels and genotype were determined by branched DNA signal amplification assay and genotype‐specific polymerase chain reaction in 43 patients with chronic active hepatitis C. Response to recombinant interferon‐α 2α (504 million units in total) was defined as complete and sustained CR→SR, n=12), complete response followed by relapse (CR→Rel, n=17), and no response (NR, n=10), excluding dropouts (n=4). Patients who showed CR→SR had a lower HCV‐RNA level (0.438 × 106eq/ml) compared to CR→Rel (2.452 × 106eq/ml, p=0.008) and NR (4.882 × 106eq/ml, p=0.009). A higher proportion of patients with CR→SR had type 2a HCV (67%) compared to the CR→Rel (28%) and the NR (0%). There was a trend for type 1b hepatitis C virus infection to have higher serum HCV‐RNA levels. There was no correlation between pretreatment HCV‐RNA level and alanine aminotransferase. However, no relation between pretreatment HCV‐RNA level and liver histology was observed; a high proportion of patients with CAH2a showed CR→SR, compared to those with CAH2b (p=0.001). Moreover, the patients with CAH2b who had low level hepatitis C virus viremia did not show CR→SR. These data indicate that pre‐treatment serum HCV‐RNA levels, genotype and liver histology are good predictors of subsequent response to interferon‐α therapy in Japanese pat