Inclusion Criteria:
* Male or female, at least 18 years of age at the time of screening.
* Currently taking an immunosuppressant regimen based on either tacrolimus or cyclosporine. Corticosteroids such as prednisone or prednisolone are permitted as components of the immunosuppressant regimen providing the dose is not more than 10 mg/day.
* Hepatitis C virus (HCV) interferon (IFN) therapy treatment-naïve or -experienced, either pre- or post-liver or renal transplant.
* Screening HCV genotype testing indicating infection with genotype 1 or 4 (GT1 or GT4) only.
Exclusion Criteria:
* Use of everolimus or sirolimus as part of the immunosuppressive regimen within 2 months of Screening Visit.
* Use of any medications contraindicated for use with the study regimen as well as those that are contraindicated for use with either ritonavir or ribavirin within 2 weeks prior to study drugs administration or 10 half-lives (if known), whichever is longer.
* Positive test result for Hepatitis B surface antigen (HBsAg) or anti-human immunodeficiency virus antibody (HIV Ab).
* Documented history of post-transplant complications directly involving the hepatic or renal vasculature as appropriate to the organ transplanted, e.g., thrombosis of the portal vein, the hepatic artery and/or hepatic vein.
* Clinically significant abnormalities, other than HCV infection, in a subject post-transplant based upon the medical history, physical examination, vital signs, laboratory profile and a 12-lead electrocardiogram (ECG) that make the subject an unsuitable candidate for this study in the opinion of the investigator.
