This 3-arm study assessed the safety and efficacy of combination treatment with peginterferon alfa-2a + ribavirin in participants with chronic hepatitis C. Three groups of participants were studied; 1) those with elevated alanine transaminase (ALT) levels, 2) those with normal ALT levels, and 3) those with human immunodeficiency virus (HIV) co-infection. Participants with genotype 1, 4, 5 or 6 received peginterferon alfa-2a 180 micrograms (mcg) subcutaneous (SC) once weekly (qw) + ribavirin 1000-1200 milligrams (mg) orally (PO) daily (dependent on body weight) for 48 weeks. Those with genotype 2 or 3 received peginterferon alfa-2a 180 mcg SC qw + ribavirin 800 mg PO daily for 24 weeks, and all participants with HIV co-infection received peginterferon alfa-2a 180 mcg SC qw + ribavirin 800 mg PO daily for 48 weeks.

Inclusion Criteria:

• Adult participants at least 18 years of age
• Chronic hepatitis C, with detectable serum hepatitis C virus (HCV) ribonucleic acid (RNA)
• Scheduled for treatment with peginterferon alfa-2a
• Compensated liver disease
• Women in fertile age must be informed about obligation of using adequate contraception during and 6 months post treatment with ribavirin (Copegus®)
• Men with a sexual partner in fertile age must be informed about obligatory contraception preventing pregnancy during the course of treatment with ribavirin (Copegus®) as well as 6 months after treatment cessation
• Female participants in the study must have a negative pregnancy test performed not sooner than within 2 weeks preceding the planned inclusion to the study
• Men with a sexual partner in fertile age must produce a negative result of the partner's pregnancy test performed not sooner than within 2 weeks preceding the planned partner's inclusion to the study

Exclusion Criteria:

• Chronic liver disease other than chronic hepatitis C
• Active hepatitis A virus or hepatitis B virus infection
• Therapy with any systemic antiviral, antineoplastic or immunomodulatory treatment less than or equal to (<=) 6 months prior to first dose of study drug
• Hemoglobin <120 grams per liter (g/L) in female participants or <130 g/L in male participants (the result must not be older than 2 weeks prior to inclusion to the study)
• Platelet count <90 x 10^9/liter (the result must not be older than 2 weeks prior to inclusion to the study
• Neutrofil count <1.5 x 10^9/liter (the result must not be older than 2 weeks prior to inclusion to the study)
• Participants with increased risk of anaemia, or participants at risk of serious health problems resulting from anaemia or decrease of hemoglobin (e.g., participants with serious cardiovascular or cerebrovascular disease)
• History or presence of a serious mental disease, especially depression, which, in the investigator's opinion, does not allow administration of peginterferon alfa-2a (Pegasys®)
• History or presence of a disease consequent to immunodeficiency (e.g., inflammatory diseases of intestine, idiopathic thrombocytopenic purpura, systemic lupus erythematosus, rheumatoid arthritis)