Oxidative stress and impaired bioactivity of nitric oxide (NO) play an important role in the organ pathogenesis and angiopathic complications of diabetes mellitus. In this study, we evaluated the effects of a-lipoic acid (ALA) on nitric oxide synthase (NOS) in lung tissues. ALA is a strong antioxidant. We wonder how it can affect oxidative stress and NO in the lung cells and vessels of diabetic rats. Wistar rats were divided into four groups; control, diabetic [65 mg/kg streptozotocin (STZ) for 15 days], STZ+ALA-treated (65 mg/kg ALA every 2 days for 15 days), and ALA-only-treated animals. At the end of the experimental period, lipid peroxidation, superoxide dismutase (SOD), and inducible NOS (iNOS) and endothelial NOS (eNOS) distribution were evaluated. Oxidative stress decreased with ALA in diabetic animals, and SOD also increased with ALA. iNOS and eNOS increased in diabetic animals, and ALA prevented iNOS increment in lung tissues. As a result, ALA can prevent some diabetic effects on the lungs and can also protect from vascular damages. (c) 2008 Elsevier Inc. All rights reserved.