Effects of nicotine, and nicotine+vitamin E on glutathione reductase (Glutathione: NADP(+) oxidoreductase, EC 1.8.1.7) activity in the muscle, heart, lungs, testicles, kidney, stomach, brain and liver tissues were investigated in vivo and also in vitro. The groups were: nicotine [0.5 mg/kg/day, intraperitoneal (i.p.)]; nicotine+vitamin E [75 mg/kg/day, intragastric (i.g.)]; and control group (receiving only vehicles). There were eight rats per group and supplementation period was 3 weeks. The results showed that nicotine (0.5 mg/kg, i.p.) inhibited glutathione reductase activity significantly in the liver, lungs, heart, stomach, kidney, and testicles by approximately 61.5%, approximately 65%, approximately 70.5%, approximately 72.5%, approximately 64% and approximately 71.5%, respectively, while it had activated glutathione reductase activity in the brain by approximately 11.8%, and had no effect on the muscle glutathione reductase activity. Vitamin E supplementation prevented this nicotine-induced decrease in glutathione reductase activity in liver, lungs, heart, stomach, and kidney. However, it did not prevent this nicotine-induced decrease in testicles. In vitro studies were also carried out to elucidate the effects of nicotine and vitamin E on glutathione reductase activity. In vitro results correlated well with in vivo experimental results in liver, lungs, heart, stomach, and testicular tissues. These results show that vitamin E administration generally restores the inactivation of glutathione reductase activity due to nicotine administration in various rat tissues in vivo, and also in vitro.