The impairment of endothelial function in hypercholesterolaemic animals and humans is known to be reversed by intravenous infusions of L-arginine (L-ARG), the precursor of NO. 22 patients with peripheral arterial obstructive disease (PAOD) received L-ARG (60 mmol) as intravenous infusions, each lasting three hours, daily for seven consecutive days. This treatment resulted in elongation of the painfree and maximum walking distances, as well as shortening of the period of time required for pain relief after walking the maximum distance. A rise in the ankle/arm pressure ratio (AAPR) was associated with an increase of arterial blood flow in both calves. The transcutaneous oxygen tension (tcpO2) in the ischaemic foot was also increased. After the 1st and the 7th infusion of L-ARG the spontaneous (PAR) as well as the ADP- and collagen-induced platelet aggregation were suppressed, the euglobulin clot lysis time (ECLT) shortened, plasma levels of platelet activator inhibitor (PAI) decreased, and cGMP levels increased. These data indicate beneficial effects of L-ARG as a therapeutic agent in patients with PAOD. We presume that in these patients high doses of exogenous L-ARG can be partially converted to NO.