OBJECTIVE To evaluate the clinical effect and side-effect of interferon-alpha (IFN-a) and ribavirin (RBV) combination therapy for Chinese patients with co-infection of hepatitis C virus (HCV) and human immunodeficiency virus (HIV), and to compare them with only HIV infection patients. METHODS 10 patients with HCV-HIV and 17 patients with only HCV infection received 5 million units of IFNalpha-2b every other day intramuscularly, and 300 mg RBV orally three times a day. Dynamic observations were done for HCV RNA and HIV RNA loads, CD4+ and CD8+ T lymphocyte counts, liver function and blood cell measures, and the side-effects of the medicines. RESULTS After 12 weeks and 24 weeks of IFNalpha and RBV combination therapy, mean HCV RNA levels reduced 1.14 log (t = 3.843, P < 0.01) and 2.08 log (t =6.564, P < 0.01) from the baseline at week 0 in the HCV-HIV co-infection group, and reduced 1.48 log (t = 6.438, P less than 0.01) and 2.33 log (t = 7.343, P < 0.01) in the HCV infection group. Meanwhile, the HIV RNA levels decreased 1.22 log (t = 3.662, P < 0.01) and 1.73 log (t = 6.119, P < 0.01) from the base line. However, there were no obvious different changes among T lymphocyte counts of HCV-HIV and HCV patients at week 0, week 12 and week 24. All 27 patients showed satisfactory biochemical response to therapy. There were some mild or moderate influenza-like symptoms, intestinal discomfort and decreased blood cell counts in the early stages of the treatments. No neuropsychic and auto-immune disorders were found. CONCLUSIONS IFNalpha-2b and RBV combination therapy showed similar anti-HCV effects during the 24 week treatment for HCV-HIV and HCV infected patients, and some anti-HIV effect was also observed. No obvious different biochemical responses and side-effects were found between the above two groups.