The blood galactose concentration was assayed by a galactose oxidase method and intravenous galactose test was performed for liver disease patients. 1. Immediate deproteinazation was necessary after the blood sample was drawn because of rapid decrease of galactose concentration in the whole blood. The color development after the addition of galactose oxidase in the developing system took 3 to 4 hours when the concentration of galactose was 10mg/dl or less. 2. A standard curve was straight when the concentration was 60mg/dl or less. But another standard curve was necessary when the concentration was 2 to 3 mg/dl. 3. A blood galactose concentration was about 0.5mg/dl befor the galactose infusion. 4. A galactose tolerance test was performed by measuring blood galactose every 15min. for four times after the infusion of 175mg/Kg body weight. A galactose disappearance curve showed straight line in 72 out of 74 cases except 2 cases, in which cases galactose T(1/2) could not be determined. 5. The mean value of galactose T(1/2) in 10 normal cases was 10.5±1.9min. and normal upper limit was determined to be 14min. (mean +2 S.D.). 6. The galactose T(1/2) correlated well with concentrations at 45min. and 60min. which could be markers of a galactose tolerance test. 7. No side effect was noticed in the performance of the galactose tolerance test.