While several viruses have been identified as agents of liver inflammation, some proportion of cases of acute hepatitis are seronegative and show no evidence of prior infection with known hepatitis viruses A, B, C, or E. Seronegative acute hepatitis is often complicated by autoimmune phenomena or late severe consequences, especially fulminant hepatitis of childhood and post-hepatitis aplastic anemia. Efforts in the Hematology Branch to identify an infectious agent in these latter two syndromes have been unsuccessful, probably because they are immune-mediated and also accompanied by massive tissue destruction. We now propose systematic collection of blood and fecal samples from patients with seronegative acute hepatitis for purposes of virus identification research. Samples will be collected from patients in United States Army clinics; patient identifiers will be employed.