The hemodynamic effects of human adrenomedullin were investigated in anesthetized Wistar rats. Intravenous administration of adrenomedullin (1.0 nmol/kg) caused a rapid and marked reduction in mean blood pressure associated with a decrease in total peripheral resistance. This reduction in mean blood pressure was closely correlated with the decrease in total peripheral resistance. These findings indicate that human adrenomedullin is a potent vasodilator and may have some role in the regulation of blood pressure.