The objective of the study is to evaluate, in each group, the number of participants who achieve rapid virological response (RVR) after 4 weeks treatment with PegIntron and Rebetol. The study will also assess whether RVR is a reliable predictor of sustained virologic response (defined as undetectable viral load at 24 weeks post-treatment).

Inclusion Criteria:

• Willing to participate in the study and sign the Informed Consent Form
• Established HCV infection, confirmed by molecular biology test (positive qualitative polymerase chain reaction [PCR] test)
• Can be treatment-naïve, have retreatment, or co-infected with HIV
• Be under treatment with PegIntron in combination with ribavirin, starting up to 14 days before the screening visit

Exclusion Criteria:

• Participants who have not confirmed their willingness to participate in the study or have refused to sign the Free and Informed Consent Form
• Prior treatment with PegIntron (combined with ribavirin or not)
• History of alcohol abuse in the past 6 months
• Decompensated liver disease
• Severe heart disease
• Decompensated thyroid disorder
• Neoplasia
• Type 1 diabetes mellitus - uncontrolled or hardly controlled
• Seizures - uncontrolled
• Primary immune deficiency
• Men and women not using appropriate contraceptive methods
• Pregnancy or lactation
• For participants co-infected with HIV: HIV-related opportunistic disease in the past 6 months or CD4 count lower than 200 cells/mm^3

Participants infected with Hepatitis C Virus (HCV) who are undergoing treatment with PegIntron and Rebetol in accordance with approved labeling at approximately 60 sites in Brazil. Participants could be treatment-naïve, undergoing re-treatment, or co-infected with Human Immunodeficiency Virus (HIV).