Guidelines for the treatment of patients infected with hepatitis C virus of genotypes 2 and 3 (HCV-2 and HCV-3, respectively) recommend a 24-week course of Peg-interferon (Peg-IFN) alpha-2a combined with ribavirin, despite 50% of patients in registration trials attaining a sustained virologic response (SVR) following Peg-IFN alpha-2a monotherapy. The aim of this study was to delineate patient characteristics that might help to identify individuals likely to benefit from ribavirin discontinuation. One hundred and forty-four HCV-2- and HCV-3-infected patients initiated Peg-IFN alpha-2a (180 microg/week) and ribavirin (1000 or 1200 mg/day); those with viral clearance at week 4 were randomized to either Peg-IFN alpha-2a monotherapy (n = 59) or continuing combination therapy (n = 61) until week 12. Overall, all but one patient with a rapid virologic response (RVR) responded by the end of therapy and the overall SVR rates were lower after discontinuation of ribavirin (54%vs 82%; P < 0.001). In RVR patients who discontinued ribavirin, low baseline viraemia helped predict SVR (odds ratio 11.2, 95% CI 2.7-47.1). SVR rates were similar in patients receiving mono- or combination therapy with low (< or =300,000 IU/mL) and intermediate viraemia (86%vs 81% and 70%vs 71%, 86% refers to low viraemic patients receiving monotherapy and 81% to those receiving combination therapy. Similarly, 70% refers to patients with intermediate viraemic levels receiving monotherapy and 71% to those receiving combination therapy), but different in those with high (>700,000 IU/mL) viraemia (37%vs 88%; P = 0.004). Thus in HCV-2- and HCV-3-infected patients, withdrawal of ribavirin and continuation of Peg-IFN alpha-2a monotherapy may be appropriate to attain an SVR, providing viraemia is cleared early during therapy and associated with low baseline viral load. These results warrant future investigations, as discontinuing ribavirin could lead to considerable savings in cost and quality of life related to over-treatment.