The present study was aimed at addressing the effect of hyperglycemia on antioxidant enzymes. The expression of catalase, superoxide dismutase and glutathione peroxidase, the three primary scavenger enzymes involved in detoxifying reactive oxygen species has been evaluated in the renal cortex of rats after 6 weeks of streptozotocin-induced diabetes. Lipid peroxidation and protein oxidation in the renal cortical homogenate were first performed to confirm a state of oxidative stress. The enzyme assays showed significant and varied alterations in catalase, superoxide dismutase and glutathione peroxidase activities. An opposing response of catalase and glutathione peroxidase activities to diabetes was observed. RT-PCR analysis was used to ascertain whether steady-state transcription levels were altered. While an increase in glutathione peroxidase and Cu-Zn superoxide dismutase mRNA parallels the increase in the activities of the enzymes, an increase in catalase gene expression in contrast to a decrease in enzyme activity suggests a role for post-translational modification in altering the activity of this enzyme.