['Patients with chronic hepatitis C virus (HCV) infection are frequently treated with a combination of pegylated interferon (peginterferon) and ribavirin. This study compared the efficacy and safety of peginterferon alfa-2a and peginterferon alfa-2b, each in combination with ribavirin.', 'A total of 320 consecutive, treatment-naive, HCV RNA-positive patients with chronic hepatitis were randomly assigned to once-weekly peginterferon alfa-2a (180 microg, group A) or peginterferon alfa-2b (1.5 microg/kg, group B) plus ribavirin 1000 mg/day (body weight <75 kg) or 1200 mg/day (body weight >or=75 kg) for 48 weeks (genotype 1 or 4) or 24 weeks (genotype 2 or 3). The primary end point was sustained virological response (SVR) by intention-to-treat.', 'More patients in group A than group B achieved an SVR (110/160 [68.8%] vs 87/160 [54.4%]; P = .008). Higher SVR rates were obtained in group A than group B among patients with genotype 1/4 (51/93 [54.8%] vs 37/93 [39.8%]; P = .04), with genotype 2/3 (59/67 [88.1%] vs 50/67 [74.6%]; P = .046), without cirrhosis (96/127 [75.6%] vs 75/134 [55.9%]; P = .005), and with baseline levels HCV RNA >500,000 IU/mL (58/84 [69%] vs 43/93 [46.2%]; P = .002). SVR rates in groups A and B were not statistically different among patients with baseline HCV RNA <or=500,000 IU/mL (52/76 [68.4%] vs 44/67 [65.7%]; P = .727) or in patients with cirrhosis (14/33 [42.4%] vs 12/26 [46.1%]; P = .774).'] Is peginterferon alfa-2a plus ribavirin more effective than peginterferon alfa-2b plus ribavirin for treating chronic hepatitis C virus infection?