Nitric oxide (NO) is a potent intra- and intercellular mes-senger involved in the control of vascular tone, neuronal signallingandhost response to infection. Inmammals,NOis synthesized by oxidation ofL-arginine catalysed by heme-proteins called NO-synthases with intermediate formation of N x -hydroxy-L-arginine (NOHA). NOHA and some hydroxyguanidines have been shown to be able to deliver nitrogen oxides including NO in the presence of various oxidative systems.