The liver function test was performed by means of two radioisotope tracer techniques in 20 normal subjects and in 63 patients with hepatobi]iary diseases. The blood disappearance rates of 131I-rose bengal and of 198Au colloid were determined by external counting method. The hepatocellular function and the hepatic blood flow were estimated from the observed data and- the results were compared with those of the conventional liver function tests. The results obtained were as follows : 1. The mean blood disappearance half time of 131I-rose bengal was 6.6¡¾0.63 minutes in normal control, 17.7¡¾6.93 in cirrhosis of the Jii er, 16.6¡¾4. 80 in acute hepatitis, and 14 7¡¾ 3. 46 in obstructive jaundice. It was markedly prolonged in the hepatobiliary disesses as compared with the normal control, but there was no significant difference among the hepatobiliary diseases. 2.The mean blood disappearance half time of 'Au colloid was 4. 0¡¾0. 66 minutes in normal control, 9.8¡¾3.42 in cirrhosis of the liver, 4.4¡¾0.82 in acute hepatitis, and 5.0¡¾1.42 in obstructive jaundice. The difference between cirrhosis of the liver and normal control was statistically significant. However, there was no definite difference among acute hepatitis, obstructive jaundice, and normal control. The mean blood disappearance rate constant (K value) was 0.177¡¾0.028/minute in normaI control, In cirrhosis of the liver, it was markedly decreased which was suggestive of the reduced hepatic blood flow. 3. The ratio of 131I-rose bengal blood disappearance half time to 'Au colloid disappearance half time was 1.68¡¾0.20 in normal contro1, 1.82¡¾0.31 in cirrhosis of the liver, 3.80¡¾0.82 in acute hepatitis, and 3.01¡¾0.54 in obstructive jaundice. The ratios in acute hepatitis and obst-ructive jaundice were remarkably higher than those in normal control and cirrhosis of the liver. 4. There was a significant correlation between the blood disappearance half time of 131I-rose bengal and that of 198Au colloid in cirrhosis of the liver. 5. In cirrhosis of the liver, the blood disappearance half times of 131I-rose bengal and of 198Au colloid were inversely correlated to the serum albumin level. In acute hepatitis, there was a good positive correlation between the blood disappearance half time of 131I-rose bengal and the serum transaminase activities. In obstructive jaundice, the blood disappearance half time of 131I-rose bengal was correlated to the serum bilirubin level.