In the present study, we investigated the effect of a nitric oxide (NO) scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide [carboxy-PTIO], on endothelium-dependent relaxation of a series of blood vessels from rabbits, such as thoracic aorta and femoral, renal, mesenteric, and pulmonary arteries, using a functional muscle bath technique. Carboxy-PTIO produced concentration-dependent contractions in various vessels. The contractile responses in renal, mesenteric, and pulmonary arteries were significantly greater than those in the aorta and femoral artery. Similarly, phenylephrine-induced contractions in renal, mesenteric, and pulmonary arteries were markedly enhanced after pretreatment with carboxy-PTIO. Also, carboxy-PTIO inhibited acetylcholine-induced relaxation in various blood vessels. The maximum inhibitions in aorta and femoral artery were significantly greater than those in renal, mesenteric, and pulmonary arteries. The present data demonstrate that carboxy-PTIO reduces basal, phenylephrine-, and acetylcholine-induced release of NO in rabbit blood vessels. However, different degrees of inhibition of endothelium-dependent vasorelaxation were observed in various vessels. Specifically, the thoracic aorta and femoral artery are less susceptible to the action of carboxy-PTIO without acetylcholine than renal, mesenteric, and pulmonary arteries. Conversely, the most potent carboxy-PTIO-induced inhibition of acetylcholine-induced vasorelaxation was observed with aorta and femoral arteries. Thus, it is suggested that the contribution of endogenous NO to vascular tone and regional blood flow may vary among different rabbit blood vessels.