The aim of the present study was to assess parameters in early phase HCV dynamics for predicting the outcome of interferon (IFN)/ribavirin combination therapy in patients with chronic hepatitis C (CH-C). Sixty-five CH-C patients who received IFN alpha-2b/ribavirin combination therapy were enrolled. The serum levels of HCV RNA 0h and 3 months after commencing therapy were serially quantified. HCV kinetic parameters such as quantity, ratio of decline, and half-life were analyzed. In genotype 1 patients, both the quantity and the ratio of decline of HCV RNA 24h after the start of therapy were useful predictors of a poor response. No patients who had serum HCV RNA above 200KIU/ml 24h after the start of therapy achieved a sustained viral response (SVR). In genotype 2 patients, conversely, these two parameters were predictors of a sustained viral response. The efficacy of these parameters in predicting the outcome of therapy was comparable to that of the disappearance of HCV RNA from sera at 4 weeks. These results demonstrate that parameters of HCV kinetics 24h after the start of therapy are useful for the early prediction of outcome in response to IFN alpha-2b/ribavirin combination therapy.