The adrenergic receptors of porcine coronary arteries were investigated in helically cut strips of small (≤0.5 mm outer-diameter (od), medium (0.8–1.2 mm od), large (1.5–2.5 mm od), and very large (>4 mm od) coronary arteries. Both the beta1agonist dobutamine and the beta2agonist terbutaline relaxed coronary arteries partially contracted by 25 mMof KCl. Dobutamine contracted small coronary arteries at 10−5 Mconcentrations, then relaxed them at 10−4 M. The beta1-adrenoceptor antagonist metoprolol contracted coronary arteries relaxed by either dobutamine or terbutaline, but the beta2antagonist H35/25 did so only in high and probably nonselective concentrations. Alpha1-adrenoreceptor stimulating concentrations of phenylephrine did not contract any of the arteries. Metoprolol and high concentrations of H35/25 further contracted large coronary arteries partially contracted by 25 mMpotassium. These contractions were blocked by verapamil and papaverine but not by atropine, phentolamine, yohimbine, mepyramine, or methysergide. This seems to indicate that beta-adrenergic receptors in porcine coronary arteries are beta1-receptors, or closely resemble beta1-receptors. They differ from many other beta1-receptors, however, in that they are stimulated by terbutaline. Alpha1adrenoreceptors seem not to be present in these porcine coronary arteries to a significant extent. Metoprolol and high concentrations of H35/25 have a direct contractile effect in large porcine coronary artery that is not mediated by alpha-adrenergic, muscarinic, histaminergic, or serotonergic receptors but requires verapamil-sensitive calcium.