BACKGROUND & AIMS: BI 207127 is a potent non-nucleoside hepatitis C virus (HCV) NS5B polymerase inhibitor in vitro. METHODS: In this double-blind, placebo-controlled study, 57 HCV genotype (GT)-1 patients (n=27 treatment-naive [TN]; n=30 treatment-experienced [TE]) with compensated liver disease were randomised for 28-day treatment with 400, 600, or 800 mg BI 207127 three times daily (TID) or placebo (only TN) in combination with peginterferon alfa 2a and ribavirin (PegIFN/RBV). Plasma HCV RNA was measured by Roche COBAS TaqMan assay. RESULTS: HCV RNA decreased in a dose-dependent manner with little difference between 600 mg (TN 5.6 log(10), TE 4.2 log(10)) and 800 mg (TN 5.4 log(10), TE 4.5 log(10)). Rapid virological response (RVR; HCV RNA 1 log(10) from nadir) in the TN groups, whereas 3/30 TE patients experienced breakthrough due to P495-mutations. Gastrointestinal adverse events (AEs) and rash were the major AEs and most frequent at higher doses. One and four patients discontinued due to AEs in the 600 and 800 mg groups, respectively. Overall, tolerability was good and better at 600 mg than 800 mg. CONCLUSIONS: BI 207127 in combination with PegIFN/RBV demonstrated strong antiviral activity with a favourable safety and tolerability profile. The best benefit/risk ratio was observed at 600 mg.