1. The effects of 11 week treatments with the new hydroxy3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor fluvastatin on renal intrinsic anti-oxidant enzyme (AOE) activities and renal function were evaluated in streptozotocin (STZ)-induced diabetic rats. 2. Renal intrinsic AOE activities, creatinine clearance and urinary albumin excretion were examined in STZ-induced diabetic rats. The levels of total cholesterol (TC), triglyceride (TG) and phospholipid (PL) were also examined. 3. In general, renal AOE activities and function were lower in diabetic rats than in non-diabetic Sprague-Dawley rats. 4. Decreases in TC, TG and PL levels and urinary albumin excretion by the HMG-CoA reductase inhibitor fluvastatin improved renal function and produced a non-uniform alteration in renal AOE; only glutathione peroxidase (GSH-Px) activity increased significantly with fluvastatin treatment. 5. It appears that the improvement in renal function and albuminuria may be related to increases in GSH-Px activity, but there was no correlation between changes in renal function and changes in the activity of Mn-superoxide dismutase or catalase.