The vasodilator action of CV-705 was investigated in a number of vascular regions of anesthetized mongrel dogs and this action was compared with that of papaverine. When CV-705 was administered intravenously the vertebral, common carotid and internal carotid blood flow was increased considerably and was long-lasting. These effects were most remarkable among the regions tested. Femoral, aortic and coronary blood flow were also increased. On the other hand, the blood flow through superior mesenteric artery and portal vein increased only slightly. Renal blood flow was decreased slightly after an intravenous administration, whereas an increase was observed after an intra-arterial administration. Such a regional distribution of blood flow after CV-705 was quite similar to that observed with papaverine. CV-705 was well absorbed through the digestive tract. CV-705 given intravenously showed a weak hypotensive and positive chronotropic action. The increase in common carotid blood flow induced by intra-arterial administration of CV-705 was not affected by pre-treatment with atropine or triprolidine, but was partially suppressed by pre-treatment with propranolol. These results suggest that CV-705 has a papaverine-like action as well as a weak beta-adrenoceptor stimulating action, consequently a vasodilator action occurs.