The aim of the present study was to compare the response to recombinant human alpha-2 interferon therapy in 2 groups of Egyptian patients having chronic hepatitis C with or without associated schistosomiasis. Group 1 included 36 patients with associated intestinal schistosomiasis, and group 2 included 24 patients without schistosomiasis. All patients had abnormal serum aminotransferase levels and were negative for hepatitis B surface antigen and anti-hepatitis core antibody, but positive for hepatitis C virus antibody in serum. All patients received interferon at a dose of 3 million units subcutaneously 3 times a week for 6 months and were followed up clinically, biochemically and haematologically during this treatment period and for 6 months thereafter. A second liver biopsy was obtained from every patient after the completion of interferon therapy. Both the percentage of complete response with return to normal of alanine aminotransferase levels during therapy and the overall response rate at 6 months (when patients with a partial response were also included as responders) were significantly lower (P < 0.001) in group 1 (14% and 33% respectively) than in group 2 (63% and 71% respectively). The liver histology also improved significantly in group 2 (46%) compared with group 1 (14%) after completion of therapy (P < 0.05). On the other hand the overall relapse rate in responders, by 6 months after cessation of therapy, was significantly higher (P < 0.05) in group 1 (92%) than in group 2 (59%). These results show that the presence of associated schistosomiasis has to be considered as an important factor in determining the response of Egyptian patients with chronic hepatitis C to therapy with interferon.