The small intestine exhibits numerous morphological and functional alterations during diabetes. Oxidative stress, a factor implicated in the pathogenesis of diabetic complications may contribute towards some of these alterations. We therefore investigated the occurrence of oxidative stress in the small intestine during diabetes by measuring the extent of oxidative damage as well as the status of the antioxidant defense system. Significant increases in lipid peroxidation (four-fold) as measured by TBARS and protein oxidation (38%) as measured by protein carbonyl content were observed after 6 weeks of diabetes. A distinct elevation in the activities of catalase (123.9%) and superoxide dismutase (71.9%) and a decline in the activity of glutathione peroxidase (67.7%) were also observed. The steady state mRNA levels of these enzymes measured by RT-PCR were, however, unchanged suggesting the absence of transcriptional control. In contrast, no changes in the levels of protein and non-protein thiols as well as the activities of glutathione reductase and glutathione-S-transferase were detected. Interestingly, decreases in the activities of xanthine oxidase (XO; 25.7%) and xanthine dehydrogenase (XDH; 42.6%) indicate that they do not contribute significantly to oxidative damage. The results thus reveal the occurrence of oxidative stress in the small intestine during diabetes and suggest its possible involvement in some of the accompanying functional alterations.