1 Using subtype-selective 5-HT 1 receptor agonists and/or the 5-HT 1 receptor antagonist GR127935, we characterized in vitro the 5-HT receptor that mediates the contraction of human and bovine cerebral arteries. Further, we investigated which sumatriptan-sensitive receptors are present in human coronary artery by reverse-transcriptase polymerase chain reaction (RT ± PCR). 2 Agonists with anity at the 5-HT 1B receptor, such as sumatriptan, alniditan and/or IS-159, elicited dose-dependent contraction in both human and bovine cerebral arteries. They behaved as full agonists at the sumatriptan-sensitive 5-HT 1 receptors in both species. In contrast, PNU-109291 and LY344864, selective agonists at 5-HT 1D and 5-HT 1F receptors, respectively, were devoid of any signi®cant vasocontractile activity in cerebral arteries, or did not aect the sumatriptan-induced vasocontraction. The rank order of agonist potency was similar in both species and could be summarized as 5-HT=alniditan4sumatriptan=IS-159444PNU-109291=LY344864. 3 In bovine cerebral arteries, the 5-HT 1 receptor antagonist GR127935 dose-dependently inhibited the vasoconstrictions elicited by both 5-HT and sumatriptan, with respective pA 2 values of 8.0 and 8.6. 4 RT ± PCR studies in human coronary arteries showed a strong signal for the 5-HT 1B receptor while message for the 5-HT 1F receptor was weak and less frequently detected. Expression of 5-HT 1D receptor mRNA was not detected in any sample.5 The present results demonstrate that the triptan-induced contraction in brain vessels is mediated exclusively by the 5-HT 1B receptor, which is also present in a majority of human coronary arteries. These results suggest that selective 5-HT 1D and 5-HT 1F receptor agonists might represent new antimigraine drugs devoid of cerebro-and cardiovascular eects.