This volume explores the biological activity and potential clinical uses of nitric oxide (NO), a gas that plays important roles in the regulation of blood pressure, the immune system, and brain function. It reviews the potential beneficial effects of nitric oxide, cGMP, and phospho-diesterases, in addition to their role as endothelial-dependent relaxing factor. Novel actions of NO and cGMP discussed in this volume include anti-apoptosis, the preconditioning adaptation mechanism, cardio- and neuro-protective effects, anti-viral or anti-protease effects, and a possible role of cGMP in gene expression/induction. The known detrimental actions of iNOS (NOS2), peroxynitrite, and reactive nitrogen species are discussed. The results of safety and clinical trials of several newly designed nitric oxide compounds with potential anti-inflammatory activity are disclosed.