Bradykinin (BK, 0.05 micrograms/kg) or glyceryl trinitrite (5 micrograms/kg) injected into the left circumflex coronary artery of anaesthetized, open-chest greyhounds, caused pronounced increases in large coronary artery diameter (CD) and coronary blood flow (CBF), whereas des-Arg9-BK (0.05-0.3 micrograms/kg), a selective bradykinin B1 agonist, dose dependently elevated CBF but had little effect on CD. BK-induced increases in CD and CBF were not affected by the intracoronary infusion of a selective B1 receptor antagonist, des-Arg9-[Leu8]BK (40 micrograms/min), but were significantly reduced by the infusion of a selective B2 receptor antagonist, D-Arg0-[Hyp3,Thi5,8,D-Phe7] BK (10-12 micrograms/min). The antagonism was reversible and specific for BK since responses to glyceryl trinitrate were not affected. Bilateral vagotomy (n = 3) or autonomic blockade with atropine (0.1 mg/kg i.v.) and propranolol (1 mg/kg i.v.) (n = 5) resulted in significant attenuation of BK-induced increases in CBF but not that of CD. It is concluded that BK is a potent dilator of both conductance and resistance coronary vessels in anaesthetized greyhounds. The dilatation of conductance vessels appears to involve a selective interaction with B2 receptors, while BK-induced increase in CBF may be mediated by both B1 and B2 receptors and involve participation of neuroreflex mechanisms.