Asian patients with chronic hepatitis C (CHC) are known to have better virological responses to pegylated (Peg) IFN-based therapy than Western patients. Although IL28B gene polymorphisms may contribute to this difference, whether favorable hepatitis C virus (HCV) kinetics during treatment plays a role remains unclear. We enrolled 145 consecutive Taiwanese patients with CHC receiving Peg-IFN α-2a plus ribavirin for the study. Blood samples were taken more frequently at defined intervals in the first 3 d. Peg-IFN was administered at week 1. It was then administered weekly in combination with daily ribavirin for 24 or 48 wk. A mathematical model fitted to the observed HCV kinetics was constructed, which could interpret the transient HCV titer elevation after Peg-IFN treatment. The results demonstrated a comparable viral clearance rate (c = 3.45 ± 3.73) (day −1 , mean ± SD) but lower daily viral production rate (P = 10 6 -10 12 ) in our patients than those reported previously in Western patients. Of 110 patients with a sustained virological response (SVR), 47 (43%) had a transient elevation of viral titer within 12 h (proportion of 12 h/3 d: 44% in non-SVR vs. 70% in SVR; P = 0.029). Among 91 patients with available rs8099917 data, patients with the TT genotype had an early surge of viral titer after therapy and a higher SVR and viral clearance rate than those with the GT genotype. In conclusion, Taiwanese patients with CHC receiving Peg-IFN plus ribavirin therapy have a lower daily viral production rate than Western patients, and the rs8099917 TT genotype may contribute to the increased viral clearance rate and better virological responses in these patients. H epatitis C virus (HCV) infection is the major etiology of chronic liver disease, liver cirrhosis, and hepatocellular carcinoma (1, 2). According to the estimate from the World Health Organization, there are more than 180 million chronic HCV-infected persons worldwide (1-3); hence, effective treatment of chronic hepatitis C (CHC) is important. Nevertheless, the current standard of care for CHC using pegylated (Peg) IFN plus ribavirin is expensive, is effective in only a certain proportion of patients who have CHC, and has many unpleasant adverse effects (4, 5). Therefore, identifying predictive factors of therapeutical response in patients with CHC is important.Several factors have been linked to the therapeutical response of patients who have CHC, including viral factors (6-11), host factors (12-15), metabolic factors (16-18), histological factors (19), types of regimen (4), and duration of infection (20). Among these factors, viral kinetics following antiviral therapy has become widely accepted in both clinical trials and daily practice (21) and increasingly recognized as the most outweighing predictor of sustained virological response (SVR) to IFN-based therapy (22). Using mathematical models of hepatitis C viral kinetics may further clarify the mechanisms of antiviral therapy, the evolution of resistant viral strains, and the length of time necessary to er...