. Peroxynitrite and hydroxyl radicals are potent initiators of DNA single-strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly(ADP ribose) polymerase (PARP). In response to high glucose incubation medium in vitro, or diabetes and hyperglycemia in vivo, reactive nitrogen and oxygen species generation occurs. These reactive species trigger DNA single-strand breakage, which induces rapid activation of PARP. PARP in turn depletes the intracellular concentration of its substrate, NAD+, slowing the rate of glycolysis, electron transport, and ATP formation. This process results in acute endothelial dysfunction in diabetic blood vessels. Accordingly, inhibitors of PARP protect against endothelial injury under these conditions. In addition to the direct cytotoxic pathway regulated by DNA injury and PARP activation, PARP also appears to modulate the course of inflammation by regulating the activation of nuclear factor &#51B, and the expression of a number of genes, including the gene for intercellular adhesion molecule 1 and the inducible nitric oxide synthase. The research into the role of PARP in diabetic vascular injury is now supported by novel tools, such as new classes of potent inhibitors of PARP and genetically engineered animals lacking the gene for PARP. Pharmacological inhibition of PARP emerges as a potential approach for the experimental therapy of diabetic vascular dysfunction.