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adrenergic blocking effects of optical isomers of methoxamine and isopropylmethoxamine. J. Pharmac. exp. Ther. 156: 445-451, 1967. Beta adrenergic receptor blocking actions of (-) and (+) isomers of methoxamine and related compounds were investigated in isolated guinea-pig tracheal chain preparations. (-)-Isoproterenol was used as the agonist and tissue was exposed to antagonist for 3 mm. All agents except (+)-isopropylmethoxamine produced a concentration-dependent parallel shift of dose-response curves of the agonist to the right. pA2 values for (-)-isopropylmethoxamine, (-)-methoxamine and (+)-methoxamine were 6.53, 625 and 4.37, respectively. ( ±)-Desoxymethoxamine also was found to produce a significant blockade of beta adrenergic receptors. The pA2 value for (±)-desoxyisopropylmethoxamine was 4.85 and that for (±)-desoxymethoxamine was 5.09. (±)-Desoxymethoxamine was found to have approximately the same activity as methoxamine, whereas (±)-desoxyisopropylmethoxamine was much more active than (+)-isopropylmethoxamine. Since the introduction of dichloroisopro-terenol as an antagonist to the inhibitory ef-fects of catecholamines (Powell and Slater, 1958), a number of structurally related chem-icals have been synthesized and tested for beta adrenergic blocking activity (Black an