Ten cases are reported of short incubation (one to four weeks) non-A, non-B hepatitis occurring after infusion of various preparations of factor VIII concentrates into patients with coagulation disorders. Five patients were symptomatic and, in all, serum transaminase levels were increased for at least six months. These cases of chronic hepatitis exhibited none of the features of autoimmune chronic hepatitis: autoantibodies were negative and serum immunoglobulins were normal. Hepatic histology confirmed acute hepatitis in two cases biopsied early in the illness, and chronic active hepatitis (three) of chronic persistent hepatitis (two) in five cases studied later. Lobular inflammation was a prominent feature in all cases. Other features not commonly associated with type A or B hepatitis included fatty change and damaged bile ducts.