The purpose of this study is to evaluate what happens to hepatitis C virus in response to treatment with pegylated interferon and ribavirin in patients with HCV compared to those with HIV and HCV.

This research is being done to help us identify how the composition of HCV changes with interferon in different populations. We will examine how quickly HCV is cleared from your body and what factors may influence that clearance. This information may help us find better treatments for HCV.

All patients who participate in this study will have frequent blood drawn in order to measure how quickly HCV virus declines. Pegylated interferon and ribavirin are not provided by the study, but will be obtained as part of standard of care treatment for hepatitis C. Participants must be willing to spend 48 hours in the hospital for frequent blood draws. They will be compensated for their time.

All patients must be HCV genotype 1. All patients must have a liver biopsy prior to enrollment into study. (This is not provided by the study).

HIV-infected patients must have a CD4 cell count>300. If HIV-infected and on antiretroviral therapy for HIV, they must be on a stable regimen for 12 weeks. The HIV regimen can not include didanosine (Videx).

Inclusion Criteria:

1. HCV infection, as documented by the presence of circulating levels of HCV RNA by any RT-PCR or bDNA assay performed by a laboratory with a CLIA certification or its equivalent within 52 weeks prior to study entry.
2. HCV RNA >1000 IU/ml.
3. Documented genotype 1 performed by any CLIA certified lab.
4. Men and women age 18 to 65 years.
5. Ability and willingness of subject or legal guardian/representative to give written informed consent.
6. Female study volunteers of reproductive potential must be willing to use two methods of birth control in order to prevent pregnancy while on IFN/RBV.

For HIV infected patients:

1. HIV-1 infection, as documented by any licensed ELISA test kit and confirmed by Western blot at any time prior to study entry. HIV-1 culture, HIV-1 antigen, plasma HIV-1 RNA, or a second antibody test by a method other than ELISA is acceptable as an alternative confirmatory test.
2. CD4+ cell count ³ 300 cells/mm3 within the prior 12 weeks at a CLIA certified lab or its equivalent.
3. Subject may be HAART naïve, but if on HAART should be on a stable regimen for 12 weeks The HAART regimen cannot include didanosine (Videx). Interaction with ribavirin and didanosine has led to fatal hyperlactatemia in a few patients.

Exclusion Criteria:

1. Unwilling to be admitted for 48 hours for serial blood draws for virology studies.
2. Hepatitis B surface antigen (HBsAg) positivity.
3. Prior IFN -based therapy.

Additional Exclusion for HIV-infected:

1. Current symptomatic HIV disease (i.e., AIDS-defining illnesses).
2. HAART regimen that contains Videx (Didanosine). Subject may previously have been on didanosine but if on a new HAART regimen should be on the regimen for 12 weeks.

Patients with HCV genotype 1 with or without HIV-infection of any race.