This 2 part study will evaluate the efficacy and safety of 12 and 24 weeks treatment with RO5190591 (danoprevir) in combination with Pegasys and Copegus, compared to Pegasys and Copegus alone, in treatment-naive patients with chronic hepatitis C genotype 1 virus infection.In Part 1 of the study, patients will be randomized to receive either 1) RO5190591 300mg po every 8 hours, 2) RO5190591 600mg po every 12 hours, 3) RO5190591 900mg po every 12 hours or 4) placebo, in combination with standard doses of Pegasys and Copegus. If the safety and virological response data from Part 1 of the study are supportive, in Part 2 patients will be randomized to receive either 1) RO5190591 300mg po every 8 hours or 600mg po every 12 hours or 900mg po every 12 hours or 2)placebo, in combination with standard doses of Pegasys and Copegus. The anticipated time on study treatment is 24-48 weeks, and the target sample size is 100-500 individuals.

Inclusion Criteria:

• adult patients, >=18 years of age;
• chronic hepatitis C, genotype 1;
• treatment-naive.

Exclusion Criteria:

• liver cirrhosis and other forms of liver disease;
• HIV infection;
• hepatocellular cancer;
• cardiac disease.