N/AWe evaluate the regenerating capacity of rat liver according to the severity and duration of the obstructive jaundice. Also we evaluate the regenerating capacity of hepatectomized rat liver according to the duration of the obstructive jaundice. The 10 week-old Sprague-Dawley rats were used. Common bile duct ligation and sequential partial hepatectomies were done. The regenerating capacity was measured by tritiated thymidine incorporation into rat liver DNA. The rate of incorporation of thymidine into DNA in the jaundiced livers increased significantly compared with that in the sham-operated liver on day 3.In jaundiced rats, the regenerating capacity after partial epatectomy decreased markedly without a return toward normal on day 3 and kept low thereafter. The duration of obstructive jaundice may be a key factor in the regeneration of rat liver after partial hepatectomy.