The liver function test was performed by means of two radioisotope tracer techniques in 20 normal subjects and in 63 patients with hepatobiliary diseases. The blood disappearance rates of $^{131}I$-rose bengal and of $^{198}Au$ 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 $^{131}I$-rose bengal was $6.6{pm}0.63$ minutes in normal control, $17.7{pm}6.93$ in cirrhosis of the liver, $16.6{pm}4.80$ in acute hepatitis, and $14.7{pm}3.46$ in obstructive jaundice. It was markedly prolonged in the hepatobiliary diseases as compared with the normal control, but there was no significant difference among the hepatobiliary diseases. 2. The mean blood disappearance half time of $^{198}Au$ colloid was $4.0{pm}0.66$ minutes in normal control, $9.8{pm}3.42$ in cirrhosis of the liver, $4.4{pm}0.82$ in acute hepatitis, and $5.0{pm}1.42$ 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 $0.177{pm}0.028/minute$ in normal control. In cirrhosis of the liver, it was markedly decreased which was suggestive of the reduced hepatic blood flow. 3. The ratio of $^{131}I$-rose bengal blood disappearance half time to $^{198}Au$ colloid disappearance half time was $1.68{pm}0.20$ in normal control, $1.82{pm}0.31$ in cirrhosis of the liver, $3.80{pm}0.82$ in acute hepatitis, and $3.01{pm}0.54$ in obstructive jaundice. The ratios in acute hepatitis and obstructive 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 $^{131}I$-rose bengal and that of $^{198}Au$ colloid in cirrhosis of the liver. 5. In cirrhosis of the liver, the blood disappearance half times of $^{131}I$-rose bengal and of $^{198}Au$ 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 $^{131}I$-rose bengal and the serum transaminase activities. In obstructive jaundice, the blood disappearance half time of $^{131}I$-rose bengal was correlated to the serum bilirubin level.