This study investigates the sites of nitric oxide (NO) release on perivascular nerve stimulation (PNS) in organ bath experiments with isolated guinea pig pulmonary (PA) and iliac artery (IA). All the preparations were pretreated with indomethacin (10−5M), to exclude the effects of cyclo-oxygenase-generated eicosanoids. NG-nitro-L-arginine methyl ester (L-NAME, 10−6M) significantly augmented the PNS-induced adrenergic contraction and subsequently administered L-arginine (3×10−4M) reversed this augmentation in both arteries. In PA, endothelial denudation did not abolish but significantly attenuated this L-NAME-induced augmentation, while it abolished the augmentation in IA. In prostaglandin F2α-precontracted PA after blockade of both adrenergic and cholinergic effector responses, PNS induced tetrodotoxin (3×10−7M)-sensitive relaxation. This relaxation was attenuated by L-NAME (10−6M) and reversed by L-arginine (3×10−4M). But it was not abolished by endothelial denudation. On the other hand, PNS did not induce such relaxation in IA under the same conditions. The above effects of L-NAME were reproduced by bovine hemoglobin (10−5M), another NO inhibitor in both arteries pretreated with capsaicin (10−6M, 15 minutes).Thus, the suggested sites of NO release on PNS are both endothelium and perivascular nerves in PA, whereas it is only endothelium in IA.