Hepatitis C virus (HCV) infection is a global health problem, which may lead to chronic hepatitis, cirrhosis, hepatic decompensation and hepatocellular carcinoma (HCC). Recently, treatment with peginterferon alfa plus ribavirin has become the standard of care for patients with chronic hepatitis C. While genotype 2 patients can have higher sustained virologic response (SVR) rates to 80-90%, genotype 1 patients generally have low SVR rates of only 40-50%. In contrast, genotype 1 Taiwanese patients have superior SVR rates than those in Western countries. Despite the overall improved response to this combination therapy, more than 75% of patients suffer from treatment-related adverse events and the costs remain high, which make individualized therapy of paramount importance to maximize treatment response and minimize adverse events.