Elevated polyol pathway enzyme activities and oxidative stress play an important role in the development and progression of diabetic nephropathy. Here, we investigated the beneficial influence of nigerloxin, a fungal metabolite and a potent aldose reductase inhibitor and free radical scavenger in the kidney of streptozotocin-induced diabetic rats. A group of diabetic rats was orally administered with nigerloxin for 30 days (100 mg/kg). Diabetic rats showed increased lipid peroxides, advanced glycation end products (AGEs), elevated activities of polyol pathway enzymes, and lowered antioxidant defense system in kidney. Administration of nigerloxin decreased kidney lipid peroxides and AGEs. Activities of polyol pathway enzymes were reduced while activities of all antioxidant enzymes, glutathione, and ascorbic acid were elevated in the kidney of nigerloxin-treated diabetic rats. We also investigated antioxidant potential of nigerloxin in gentamicin-induced nephrotoxicity in Wistar rats. Groups of rats were orally administered with nigerloxin for 8 days (25 mg or 100 mg kg(-1) body weight day(-1)) along with gentamicin (80 mg/kg, i.p., for 8 days). Gentamicin induced increase in lipid peroxides, decrease in glutathione and activities of antioxidant enzymes in the kidney, and increase in blood creatinine, and urea concentrations were significantly countered by nigerloxin treatment. Thus, the results indicated the beneficial influence of nigerloxin on polyol pathway and oxidative stress associated with diabetes, which are implicated in ameliorating the development of diabetic nephropathy. Nigerloxin also ameliorated oxidative stress induced by gentamicin in the renal tissue.