Summary. In patients with chronic hepatitis C, rapid virological response (RVR) at week 4 of treatment seems to be strongly associated with a high probability of achieving a sustained virological response (SVR). The aim of this study was to investigate the outcome of different pegylated interferon-α2b (Peg-IFN-α2b) dosages plus ribavirin (RBV) in patients with RVR. Forty-five naïve patients chronically infected with hepatitis C virus (HCV)-1b started Peg-IFN-α2b (1.5 μg/kg/week) in combination with weight-based RBV doses (800–1200 mg/day). Thirty-one patients (68.9%) attained RVR at week 4 of therapy, while four further patients showed negative HCV-RNA values for the first time at week 12 and were considered early virological responders (EVR). The 31 RVR patients were randomized to receive either RBV plus 1.5 μg/kg/week (17 pts) or 1.0 μg/kg/week (14 pts) of Peg-IFN-α2b for the remaining 44 weeks. The two groups were matched for age, sex, baseline alanine aminotransferase levels, viral load and fibrosis score. After 6 months of post-treatment follow-up, the prevalence of SVR was 94.1% (16/17) among RVR patients treated with 1.5 μg/kg/week and 92.8% (13/14) in RVR patients treated with 1.0 μg/kg/week (P = not significant). A high-baseline viral load (P = 0.01) and bridging fibrosis/cirrhosis (P = 0.02) negatively influenced the likelihood of achieving RVR. On the contrary, the ability of RVR patients to achieve SVR did not correlate with these baseline characteristics in either of the treatment group. Finally, the SVR rate among EVR patients who responded after more than 4 weeks of treatment was significantly lower than among RVR patients (1/4 = 25%vs 29/31 = 93.5%; P = 0.0058), because of a high prevalence of post-treatment relapse among patients with EVR.