This randomized, double-blind, placebo controlled, 3 part study will assess the safety, tolerability and pharmacokinetics of RO5303253 in healthy volunteers and patients with chronic hepatitis C genotype 1. In Part A, cohorts of healthy volunteers will be randomized to receive single ascending doses of RO5303253 or placebo. In Part 2, healthy volunteers will receive a single dose of RO5303253 or placebo in a cross-over design (with a washout period of at least 7 days) to assess food effects on pharmacokinetics. In Part 3, patients with chronic hepatitis C will be randomized ro receive either RO5303253 or placebo for 5 days.

Inclusion Criteria:

• Healthy volunteers or patients with chronic hepatitis C genotype 1, 18 to 60 years of age
• Patients must be treatment-naïve for antiviral therapy for chronic hepatitis C with interferon based therapy
• Body mass index (BMI) 18 - 32 kg/m2 inclusive, minimum weight 45 kg
• Females must be surgically sterile or menopausal
• Male subjects and their partners of childbearing potential must use 2 methods of contraception throughout the study and for 70 days after the last dose

Exclusion Criteria:

• Pregnant or lactating women and male partners of women who are pregnant or lactating
• Women with reproductive potential
• Positive for hepatitis B or HIV (or hepatitis C for healthy volunteers) at screening
• For hepatitis C patients: decompensated liver disease or impaired liver function, evidence of cirrhosis documented at any time, presence or history of non-hepatitis C chronic liver disease