Because both vasodilation induced by adrenomedullin (AM) and that induced by calcitonin gene-related peptide (CGRP) may occur via the same receptor, the two peptides might play similar roles in circulation. To examine this possibility, we used the colored microsphere technique and an ultrasonic flowmeter to investigate the systemic and regional effects of an equivalent dose (650 pmol/l) of AM and CGRP in conscious Wistar rats. AM significantly decreased mean arterial pressure and peripheral resistance but increased heart rate and cardiac index (CI). On the other hand, hypotension induced by CGRP was not accompanied by an increment in Cl. Both AM and CGRP increased the femoral arterial blood flow measured by the flowmeter, with the increase by AM being significantly larger. The regional hemodynamic effects were quite different between the two peptides. AM increased the blood flow in the heart, lungs, kidneys, adrenal glands, and spleen, whereas CGRP increased blood flow only in the heart. On the other hand, CGRP increased the cutaneous and gastric blood flows, which were not affected by AM. These differences in the regional vasodilatory effects of AM and CGRP suggest that the two peptides do not play similar roles in circulatory regulation.