Objective: Endogenous vasodilatory peptides VIP (vasoactive intestinal polypeptide) and PACAP (pituitary adenylate cyclase activating peptide) partially share receptors. Both VIP and the PACAPs activate the VPAC₁ and VPAC₂ receptors, whereas the PAC₁ receptor is dedicated to the PACAPs. Contrary to VIP, infusion of PACAP-38 in migraineurs causes a delayed-phase migraine-like attack. This difference calls for further investigation of the distribution and effect of the intracranial receptors for these peptides. Methods: The vascular effect of VIP, PACAP-27 and PACAP-38 was examined by wire myograph experiments on the isolated, precontracted middle cerebral artery (MCA) and basilar artery (BA) of the rat. The vasodilatory effect was challenged with peptide antagonists for the VPAC₁ and/or VPAC₂ receptors. Preliminary experiments were done with the pure PAC₁ peptide agonist Maxadilan. mRNA expression of the receptors VPAC₁, VPAC₂ and PAC1 in the MCA, BA and middle meningeal artery (MMA) of the rat was examined by qRT-PCR. Results: VIP, PACAP-27 and PACAP-38 elicited comparable vasorelaxant action in isolated rat MCA and BA. Respective pEC50 MCA: 7.87±0.17, 7.88±0.12, 7.52±0.10, respective pEC50 BA: 8.31±0.27, 7.19±1.14, 7.81±0.17. PACAP-27 and PACAP-38 were equipotent in the two arteries, while VIP proved more potent in BA than in the MCA. The VPAC₁ antagonist PG97-269 demonstrated more efficient blocking of the relaxant effects than the VPAC₂ antagonist PG99-465 for all peptides in both vascular beds. The combination of the two antagonists blocked more efficiently than either alone. No marked dilatory effect was observed with the PAC₁-agonist Maxadilan. qRT-PCR studies demonstrated that all 3 receptors were present in the tested vascular beds, but with the PAC₁ receptor in relatively small amounts. Conclusion: Combined results indicate that the higher tendency of PACAP over VIP to cause headache is due to non-vascular effects.