Positivity for serum anti-HTLV-1 antibody (anti-HTLV-1) in 171 patients with various chronic liver diseases and 22 asymptomatic hepatitis B virus (HBV) carriers was compared with that of 200 healthy controls in the Chikugo district of Japan. The rate of anti-HTLV-1 positivity in patients with liver disease was 8.1% (14/171) and was higher than that (3.5%: 7/200) in healthy controls, but the difference was not significant. However, in patients with liver disease with a history of blood transfusion, the positive rate was 18.4% (7/38) which was significantly higher than that for healthy subject (P less than 0.001). On the other hand, in 133 liver disease patients without blood transfusion, anti-HTLV-1 positivity was significantly higher (P less than 0.05) in patients with hepatitis B surface antigen (11.3%: 6/53) than in those without it (1.3%: 1/80). These data suggest that the high incidence of anti-HTLV-1 in our patients with liver disease was due to the transmission of HTLV-1 by the same routes (maternal transmission and blood transfusion) and probably at the same time as the hepatitis viruses (HBV and hepatitis C virus).