This non-randomized, open-label study will evaluate the interaction of RO5190591(danoprevir)/ritonavir with and without ketoconazole and the safety and tolerability in healthy volunteers. Participants will be administered repeated daily doses of ketoconazole alone, RO5190591/ritonavir, and RO5190591/ritonavir plus ketoconazole. The anticipated time on study treatment is 25 days.

Inclusion Criteria:

• Adult healthy volunteers, aged 18-64 years, inclusively
• Weight >/=50.0 kg
• Body Mass Index (BMI) 18.0-32.0 kg/m2
• Ability and willingness to abstain from alcohol, xanthine-containing beverages or food (coffee, tea, cola, chocolate, "energy drinks") from 48 hours prior to entry in the clinical study center until discharge
• Ability and willingness to abstain from grapefruit or grapefruit juice, star fruit, and Seville oranges from 7 days prior to entry in the clinical study center until discharge
• Medical history without major recent or ongoing pathology

Exclusion Criteria:

• Pregnant or lactating women and male partners of women who are pregnant or lactating
• Sustained supine systolic blood pressure >140 or <90 mmHG and supine diastolic blood pressure >90 or <50 mmHG at Screening or Day -1
• Resting heart rate >100 or <45 beats per minute at Screening or Day -1
• Any history of clinically significant cardiovascular or cerebrovascular disease
• Positive drug test result at screening or each admission
• Donation or loss of blood over 450 ml (1 pint) within 60 days prior to screening