This single-dose, randomized, double-blind, double-dummy, placebo-controlled, positive-controlled four-way crossover study will evaluate the effect of a single dose of danoprevir with low-dose ritonavir on the QC/QTc interval in healthy volunteers. Subjects will be randomly assigned to one of four sequences with treatments of A: therapeutic dose of danoprevir plus ritonavir (DNV/r), B: supratherapeutic dose of DNV/r, C: moxifloxacin and D: placebo, with a washout period of at least 7 days between treatments.

Inclusion Criteria:

• Adult healthy volunteers, 18 - 60 years of age
• Female subjects must be surgically sterile or post-menopausal
• Male subjects and their partners of child-bearing potential must use to methods of contraception for the duration of the study and for three months after the last drug administration
• Agree to abstain from strenuous exercise for three days before dosing and throughout the study (including washout period and follow-up visit)

Exclusion Criteria:

• History or evidence of any clinically significant disease or disorder
• Pregnant or lactating women
• Male partners of women who are lactating or trying to become pregnant
• Current smokers or subjects who have discontinued smoking less than six months prior to first dosing
• Positive alcohol breath test; suspicion of regular consumption of drugs of abuse
• Positive for hepatitis B, hepatitis C or HIV infection
• Participation in an investigational drug, biologic, or device study within three months before first study drug administration