ACE inhibitors elicit the release of endothelium-derived relaxing factors in perfused isolated canine arteries (Mombouli and Vanhoutte, J. Cardiovasc. Pharmacol. 1991, 18: 926-927); this action is antagonized by bradykinin-receptor antagonists suggesting that it is mediated by local kinin generation. The effects of exogenous tissular kallikrein (porcine) were examined in vitro in the isolated canine coronary artery. Isometric tension was measured in blood vessel rings (with and without endothelium) contracted with prostaglandin F2 alpha. The kallikrein elicited relaxations in rings with, but not in those without, endothelium. This response was augmented by the angiotensin converting enzyme inhibitor perindoprilat, and it was antagonized by the selective B2-kinin receptor antagonist HOE 140 and aprotinin, an inhibitor of tissular kallikrein. These data suggest that in the canine coronary artery, kallikrein causes relaxations that may be mediated by kinins generated from endogenous kininogens present in the vascular wall.