One hundred six HIV-infected patients with chronic hepatitis C virus (HCV) infection were randomized to receive ribavirin (RBV) 400 mg bid plus interferon alpha-2b (IFN-alpha) at two different doses, 3 mU tiw (control arm) or 5 mU daily for the first 6 weeks, followed by 3 mU tiw until completing 6 months of therapy (induction arm). All patients had CD4 counts above 350 cells/microl and 89% were taking antiretroviral therapy. Adverse effects leading to treatment discontinuation occurred in 12.3% of patients, a rate quite similar to that seen in HCV-monoinfected patients. Negative serum HCV-RNA values (< 60 IU/ml) were recorded in 24.7% and 35.5% of patients at 3 and 6 months of therapy. However, in the intent-to-treat analysis, sustained response was reached by only 16% of patients (22.4% in the on-treatment analysis). No differences between treatment arms were noticed. Patients with HCV genotypes 2 or 3 had a 7-fold higher response rate than those with HCV genotypes 1 or 4. Therefore, early, end-of-treatment, and sustained response rates are lower in HIV/HCV-coinfected patients treated with RBV/IFN-alpha combination therapy. Since HCV-related liver disease is currently one of the leading causes of morbidity and mortality among HIV-infected patients, new treatment options are urgently needed for coinfected individuals.