Vasoactive intestinal polypeptide (VIP) has powerful vasodilating effects, shown by a striking conductance increase especially in the vertebral artery (+100%), the left descending coronary artery (+200%), the left gastric artery (+550%), the superior pancreaticoduodenal artery (+200%), and the gastroduodenal artery (+220%). The conductance increase was also significant in the common and the proper hepatic artery (+60% and 50%, respectively). Total peripheral conductance was progressively increased by 45%; arterial pressure was reduced by 20%. Blood flow was assessed with non-cannulating electromagnetic flow sensors in anesthetized dogs. VIP was injected in a brachial vein at intervals of 1 min in amounts of 1-1024 ng X kg-1, following a logarithmic scale. The pulsatile flow and pressure signals were analog-digital-converted and processed simultaneously by a computer program to obtain mean flow (ml X min-1) and mean pressure (mmHg) values for every 3 sec. The hemodynamic data were presented as conductances. No response was observed in the inferior mesenteric artery, the renal artery, or the femoral artery. Major vasoactivity thus occurred in cerebral, cardiac, gastric, hepatic, and pancreatic regions.