To study the influence of liver injury on hepatic superoxide dismutase in rats, superoxide dismutase was determined in rat liver after either CCl₄ injection or common bile duct ligation. In normal rat liver cells, 95.2% of total cellular superoxide dismutase was distributed in cytosol and 4.8% was in mitochondria, respectively. In single injection of CCl₄, cytosolic superoxide dismutase was decreased at 6 hours after injection and revealed minimum value at 24 hours, thereafter increased to 82% of the control level at 72 hours. Mitochondrial superoxide dismutase was decreased at 12 hours after injection and revealed minimum value at 24 hours while increasing to 79% of the control level at 72 hours after injection. In 2 day-interval injection of CCl₄, both cytosolic and mitochondrial superoxide dismutase showed decreased levels until 9 days after the first injection and did not recover. In 3 day-interval injectiion of CCl₄, both cytosolic and mitochondral superoxide dismutase showed decreased to levels until 6 days after the first injection and recovered to 75% and 64% of the control at 9 days, respectively. No significant changes were noted after common bile duct ligation. All of these findings are compatible with the views that cellular superoxide dismutase decreases in CCl₄-induced liver injury and decrease of cytosolic superoxide dismutase precedes that of mitochondria) superoxide dismutase. But superoxide dismutase did not change after the ligation of common bile duct.