The Nobel Prize for Medicine and Physiology 1998 was awarded to three American pharmacologists: Robert F.Furchgott, Louis J. Ignarro and Ferrid Murad for their work on nitric oxide as a signalling molecule in the cardiovascular system. This discovery is a classical case of serendipity. NO is an endothelium-derived factor which mediates local vasodilation. It protects the vascular system against atherosclerosis by various effects on leukocytes and vascular permeability. NO appears to be a universal signalling molecule in the body, involved in the inflammatory response, apoptosis and neurotransmission. Its biochemistry is closely linked to that of oxygen radicals.