The current study investigated the role of poly(ADPribose) polymerase (PARP) in the development of diabetic retinopathy. Activity of PARP was increased in whole retina and in endothelial cells and pericytes of diabetic rats. Administration of PJ-34 (a potent PARP inhibitor) for 9 months to diabetic rats significantly inhibited the diabetes-induced death of retinal microvascular cells and the development of early lesions of diabetic retinopathy, including acellular capillaries and pericyte ghosts. To further investigate how PARP activation leads to cell death in diabetes, we investigated the possibility that PARP acts as a coactivator of nuclear factor- B (NF- B) in the retinal cells. In bovine retinal endothelial cells (BRECs), PARP interacted directly with both subunits of NF- B (p50 and p65). More PARP was complexed to the p50 subunit in elevated glucose concentration (25 mmol/l) than at 5 mmol/l glucose. PJ-34 blocked the hyperglycemia-induced increase in NF- B activation in BRECs. PJ-34 also inhibited diabetes-induced increase expression ofintercellular adhesion molecule-1, a product of NF-B-dependent transcription in retina, and ubsequent leukostasis. Inhibition of PARP or NF- B inhibited the hyperglycemia (25 mmol/l glucose)-induced cell death in retinal endothelial cells. Thus, PARP activation plays an important role in the diabetes-induced death of retinal capillary cells, at least in part via its regulation of NF-B. Diabetes 53: 2960-2967, 2004