Eighteen maleWistar rats were divided into 3 groups of 6 animals each. Two groups received different intraperitoneal doses of TCDD (0.75 and 8Fg) in DMSO solution and the third group (control) received only DMSO on days 0, 7 and 14. On day 21 the animals were sacrificed, and then blood tests, pathological examination and CYP1A1 activity measurement were performed. In rats that received a high dose of dioxin (8 Fg) hepatic lobules revealed parenchymal degeneration and vacuolization of hepatocytes was observed, and also an increased CYP reaction was found in central parts of lobules, around the central vein. The reaction in control and low dose groups was weak. The resorufin level was significantly (P<0.05) higher in the group receiving a low dose of dioxin as compared to the control group. The study confirmed that TCDD damages the rat liver in a dose-dependent manner. Administration of high TCDD doses causing major liver damage also damaged CYP1A1 (based on higher resorufin levels in epiluminescence). TCDD activates CYP1A1, which was confirmed by increased immunohistochemical reactivity of central areas of hepatic lobules.