Mitochondrial respiratory function, ketogenesis and collagen metabolism of the liver in biliary obstruction and after its relief were investigated in dogs and patients with obstructive jaundice. In dogs, it was found that hepatic mitochondrial respiratory function decreased significantly with prolongation of biliary obstruction, but recovered to varying degrees depending on both the duration of obstruction and of the period after the relief of obstruction. Ketogenesis was also impaired by biliary obstruction and its recovery was found in a slight degree only in cases with short-term obstruction. Hepatic collagen content and the synthetic ability significantly increased in biliary obstruction, and returned to normal levels with a relatively short period after the relief. Analogous results were obtained in clinical cases, but the decrease in serum bilirubin was somewhat delayed and increased hepatic collagen content continued after relief of the obstruction. When major surgery is required in patients with obstructive jaundice, biliary drainage should be carried out first 4 to 6 weeks before the performance of major operations. In cases with biliary obstruction for 12 weeks or more, it is desirable to wait for more than 6 weeks after biliary drainage since recovery of hepatic function, especially mitochondrial function, will be extremely slow.