The cholinoceptor antagonists anisodamine and anisodine are widely used in the People's Republic of China for the management of acute circulatory shock but the mechanism of their beneficial effects is not fully known; we therefore investigated if these agents possessed adrenoceptor blocking properties. The antagonistic effect of anisodamine and anisodine against the specific binding of the alpha 1-adrenoceptor ligand [3H]-WB-4101 to cardiac and brain tissue membrane preparations and against the effects of phenylephrine on isolated aortic strips and left atria of rats were compared with classical muscarinic receptor and adrenoceptor blocking agents. Both anisodamine and anisodine possessed alpha 1-adrenoceptor blocking properties; the order of potency of various agents in displacing the binding of [3H]-WB-4101 to receptors and in antagonizing the effects of phenylephrine on aortic strips and left atria was: prazosin greater than atropine greater than anisodamine greater than scopolamine greater than anisodine. It is concluded that both anisodamine and to a lesser extent anisodine possess alpha 1-adrenoceptor blocking properties; this antagonistic activity of anisodamine may contribute to its salutary effects on the microcirculation. However, it is unlikely that anisodine produces a significant adrenoceptor blockade in the clinically used dose-range.