Recently, transfusion-transmitted virus (TTV) was discovered to be a potential causative agent for non-A-E hepatitis. Little is known about the relation between TTV and the clinical courses of various types of acute viral hepatitis. One hundred twenty-five patients with acute viral hepatitis who were admitted to the Chiba University Hospital between 1984 and 1998 and 100 persons with normal liver function tests were tested for the presence of TTV in their sera. Serum samples were tested for TTV DNA and genotype by polymerase chain reaction (PCR). TTV DNA was detected in 15 of 35 patients (43%) with non-A-E hepatitis, 14 of 33 patients (42%) with hepatitis C, 8 of 28 patients (29%) with hepatitis A, 7 of 29 patients (24%) with hepatitis B, and 37 of 100 subjects with normal liver function tests (37%). The detection rate did not differ statistically between non-A-E hepatitis and hepatitis A, B, C, or controls. The distribution of TTV genotypes was similar in non-A-E, A, B, C types, and controls. The clinical characteristics of the acute illnesses were similar for patients with or without TTV in hepatitis non-A-E, A, B, or C. Although TTV was detected frequently in non-A-E acute hepatitis, no etiologic role for TTV could be established.