Serological investigations for hepatitis B surface and e antigen, antibody to hepatitis B surface, core and e antigen and antibody to hepatitis A virus were carried out in 22 patients with fulminant hepatitis admitted to Medical Department A, Rigshospitalet, Copenhagen, in 1970-77. Nine patients had hepatitis type B and four type A. One patient had evidence of both type A and B infection, whereas the remaining eight patients showed no evidence of type A or B infection. Two of these had been treated with disulfiram and a drug aetiology could not be excluded, but in six patients no known cause of fulminant hepatitis could be determined and these patients were classified as having hepatitis type non-A non-B. The survival rate was not statistically different for patients having type A, B, or non-A non-B hepatitis.