An intravenous galactose tolerance test with single injection of galactose of 175 mg/Kg body weight were performed in the patients with various liver diseases who admitted to The Okayama University Hospital, and half time of galactose disappearance (Gal T(1/2))was obtained. 1. The normal value of Gal T(1/2) was 10.5±1.9 min. and Gal T(1/2) values in the patients with acute hepatitis in icteric stage and in convalescent stage were 14.2±6.9 and 11.3±1.3 min. In the patients with chronic hepatitis and precirrhosis, Gal T(1/2) were 11.4±1.5 and 13.3±1.9 min., respectively. Gal T(1/2) values in cirrhotic patients were remarkably elevated up to 22.3±7.1 min. In patients with extrahepatic obstructive jaundice, Gal T(1/2) values were 12.4±2.4 min. and patients with intrabepatic cholestasis and fatty liver had normal Gal T(1/2) values. However, 2 out of 5 patients of extrahepatic obstructive jaundice showed elevated value of Gal T(1/2), in which cases secondary biliary cirrhosis was revealed at autopsy. 2. Gal T(1/2) values were closely correlated with KICG values and Gal T(1/2)/ICG T(1/2) value was appeared to be a marker for the differential diagnosis of parenchymal and obstructive jaundice. 3. Gal T(1/2) values were correlated well with KICG, BSP, serum albumin, serum gamma globulin, A/G ratio, ZST and blood NH(3) levels, but were not correlated with total serum bilirubin levels, ALP and S-GOT activities. 4. Histological examination showed that the elevation of Gal T(1/2) values were closely correlated with the development of fibrosis, disarrangement of hepatic lobules and hepatic cell necrosis. 5. The peritoneoscopic observation indicated that the Gal T(1/2) value appeaared to increase in parallel with completion of the nodular formation on the liver surface.