It is known that selenium compounds can restore some metabolic parameters in experimental diabetes. However, as there are no clear data about their effects on the altered antioxidant defense system of the diabetic heart, we aimed to investigate whether these beneficial effects extend to the alterations of some enzyme activities, which play important roles in antioxidant defense system. Diabetes was induced by streptozotocin (50 mg/kg body weight) and rats were then treated with sodium selenite (5 mu mol/kg/d) for 4 wk. Sodium selenite treatment of the diabetic rats significantly restored the altered activities of glutathione-S-transferase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase, which are involved in the glutathione metabolism of the heart, but slightly but significantly decreased the high blood glucose level. In summary, the present study suggests that the beneficial effects of sodium selenite treatment appears to be the result of the restoration altered activities of the antioxidant enzymes in diabetic heart tissue.