['To clarify clinical parameters predicting sustained viral response (SVR) during 48 weeks pegylated-interferon (peg-IFN)alpha-2b plus ribavirin therapy for Japanese patients with chronic hepatitis C [CH(C)] genotype 1b and high viral titers.', 'One hundred and fifty-one (151) patients receiving peg-IFNalpha-2b plus ribavirin therapy for 48 weeks were enrolled. SVR and clinical parameters were evaluated. The relationship between virological parameters (substitutions in the core and NS5A) and the degree of early viral decrease was also studied.', 'Seventy (46.4%) patients achieved SVR (per protocol analysis). Negative predictive value (NPV) of <2-log10 decrease after 4 weeks of therapy for SVR was 78.0%; similar to that for failing to achieve early viral response (EVR) at 12 weeks (82.2%).'] Is failure to achieve 2-log10 viral decrease in first four weeks of peg-IFNalpha-2b plus ribavirin therapy for chronic hepatitis C with genotype 1b and high viral titer useful in predicting non-response : evaluation of response-guided therapy?