The antagonism by pelanserin (2,4(1H,3H)-quinazolinedione,3-[3-(4-phenyl-1- piperazinyl)-propyl]-HCl), a potent 5-HT2 receptor antagonist, of alpha 1-adrenoceptor-mediated contractions of endothelium-denuded carotid, aorta, mesenteric and caudal arteries of both normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats was investigated. The selective alpha 1-adrenoceptor agonist methoxamine elicited concentration-dependent contractions in all four arterial rings, an effect which was competitively antagonized by pelanserin. pA2 values for pelanserin were in the 7.67-8.11 range when evaluated against the alpha 1-adrenoceptor agonist in arteries from normotensive or hypertensive rats. These data support the conclusion that pelanserin displays alpha 1-adrenoceptor blocking properties. The ability of the 5-HT2 receptor antagonist pelanserin to additionally block alpha 1-adrenoceptor-mediated constriction in different vessels of WKY and SHR may potentially contribute to its blood pressure lowering effects.