1. In an animal model in vivo, ginsenosides (GS), saponins from Panax ginseng, were shown to protect against myocardial ischaemia/reperfusion damage with concomitant increased 6-keto-PGF1 alpha and decreased lipid peroxidation. 2. In perfused rabbit lung in situ and isolated rabbit aortic rings, GS protected the pulmonary and aortic endothelium against electrolysis-induced free radical injury. Purified components of GS, Rb1 and especially Rg1, relaxed pulmonary vessels and this effect was eliminated by nitro-L-arginine, an inhibitor of nitric oxide (NO) synthase. 3. In cultured bovine aortic endothelial cells, GS enhanced the conversion of [14C]-L-arginine to [14C]-L-citrulline, indicating an increased release of NO. 4. As the neurotransmitter inducing penile erection, NO release was shown to be enhanced by GS in rabbit corpus cavernosum (CC) in vitro. Ginsenosides enhanced both acetylcholine-induced and transmural nerve stimulation-activated relaxation associated with increased tissue cGMP. The latter effect was eliminated by tetrodotoxin and was associated with decreased tissue cGMP. Ginsenoside-enhanced CC relaxation was attenuated by nitro-L-arginine and oxyhaemoglobin, and enhanced by superoxide dismutase. 5. It is postulated that cardiovascular protection by GS may be partly mediated by the release of NO, a potent antioxidant, and that the GS-enhanced release of NO from endothelial cells, especially from perivascular nitric oxidergic nerves in the CC, may partly account for the aphrodisiac effect of Panax ginseng used in traditional Chinese medicine.