Recently, a radical operation on jaundiced patients is performed after biliary decompression by PTCD. In this study, the mechanism of liver cell recovery after biliary decompression was studied hisologically and electron microscopically. Thirty adult dogs were used. After laporatomy, the common bile duct was doubly ligated and severed. The obstruction was released by cholecystoduodenostomy, 2 (Group 1), 3 (Group 2), 4 (Group 3) and 5 and 6 weeks (Group 4) after the operation. A liver biopsy was obtained at the second operation. Four weeks after the second operation, all dogs were sacrified. Liver specimens were taken and examined histologically and electron microscopically. Two weeks after ligation, a marked decrease in glycogen particles, moderate dilatation of bile canaliculi, swelling of Kupffer cells, edema and infiltration of inflammatory cells in the interlobular connective tissue, increase in smooth endoplasmic reticulum and enlargement of the Golgi zone were seen in Group 1. Four weeks after release of the obstruction, glycogen particles increased greatly, and smooth endoplasmic reticulum decreased. Generally, the liver cells and bile canaliculi returned to almost thier normal structure. Three weeks after ligation, similar changes occurred in Group 2 as in Group 1, although the changes were more advanced. Four weeks after release of the obstruction, the liver cells returnd to almost thier normal appearance. Four weeks after ligation, the bile canaliculi markedly dilated and microvilli disappeared in Group 3. The increase in smooth endoplasmic reticulum, enlargement of Golgi apparatus, decrease in glycogen particles and appearance of myeloid bodies were prominent. Four weeks after release of the obstruction, these changes were still observed, and the liver cells remained in the recovery process. Five or 6 weeks after ligation, similar changes in Group 4 as seen in Group 3 occurred, but the changes were more advanced. Four weeks after release of the obstruction, the liver cells had not recovered well. The liver cells recovered well 4 weeks after release of up to 3 weeks of obstruction, but ultrastructural changes still remained 4 weeks after release of over 3 weeks of obstruction.