The hepatitis C virus (HCV) and the human immunodeficiency virus (HIV) often co-infect the same individuals because they share comparable routes of transmission. Co-infection with HIV in those patients infected with HCV influences the accuracy of HCV diagnostic testing, levels of HCV viremia, severity of liver histopathology, and rate of progression to cirrhosis. By contrast, the effect of HCV co-infection on HIV disease is unclear. Nevertheless, the combination therapy containing recombinant interferon alfa-2b (rIFN-alpha 2b) plus ribavirin has been shown to be efficacious in the treatment of chronic hepatitis C, whereas alpha interferon monotherapy has been shown to be efficacious in patients co-infected with HCV and HIV. It is therefore logical to propose and test the hypothesis that combination rIFN-alpha 2b/ribavirin therapy will also benefit patients who are co-infected with HCV and HIV. A double-blind, placebo-controlled study is presently under way to investigate this hypothesis.