Aims/hypothesis: Hyperglycaemia-induced mitochondrial overproduction of reactive oxygen species (ROS) is central to the pathogenesis of endothelial damage in diabetes. R-(+)-α-lipoic acid has advantages over classic antioxidants, as it distributes to the mitochondria, is regenerated by glycolytic flux, and has a low redox potential. Methods: To assess the effect of R-(+)-α-lipoic acid on experimental diabetic retinopathy, three groups of male Wistar rats were studied: nondiabetic controls, untreated diabetic controls, and diabetic rats treated with 60 mg/kg bodyweight R-(+)-α-lipoic acid i.p. for 30 weeks. Quantitative retinal morphometry included acellular occluded capillaries and pericyte numbers. The effects of R-(+)-α-lipoic acid on parameters of oxidative and nitrative stress, AGE and its receptor and nuclear factor kappa B (NFκB) were assessed by immunoblotting, and NFκB activation by electrophoretic mobility shift assay. Angiopoietin-2 and vascular endothelial growth factors were also determined by immunoblotting. Results: After 30 weeks of diabetes, the number of acellular capillaries was significantly elevated in diabetic rats (57.1±10.6 acellular capillary segments [ac]/mm 2 of retinal area) compared with nondiabetic (19.8±5