Neuropeptide Y (NPY) is known as a potent vasoconstrictor of peripheral blood vessels both in vivo and in vitro. There have been reports suggesting that NPY also has a dilatory effect. The aim of the present study was to elucidate whether NPY dilates small human subcutaneous arteries. Subcutaneous arteries, obtained from patients undergoing abdominal surgery, were mounted in in vitro tissue baths, and the vascular responses to NPY were investigated. The presence of mRNA encoding the human NPY Y1receptor in endothelial cells from human umbilical veins was studied by the use of reverse transcriptase - polymerase chain reaction (RT-PCR). In arteries precontracted with the prostaglandin analogue U46619, NPY induced a concentration-dependent vasodilation (Emax30 ± 10% of the U46619-induced contraction), which was significantly inhibited by the NPY Y1receptor antagonist BIBP3226 (1 µM), causing a rightward shift of the concentration-response curve, pEC507.1 ± 0.3 vs. 7.7 ± 0.3 for NPY alone. After pretreatment with the nitric oxide synthetase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (10 µM), the dilation was abolished (Emax6 ± 5% of the U46619-induced contraction). mRNA encoding the human NPY Y1receptor was detected in endothelial cells from human umbilical veins. It was concluded that NPY induces vasodilation in human subcutaneous arteries. The dilation is mediated via the NPY Y1receptor and is dependent on nitric oxide.Key words: vasodilation, neuropeptide Y, BIBP3226, nitric oxide, human.