During the examination of the cardiac action of a Chinese crude drug, musk, it was found that musk selectively increased the effect of isoprenaline in catecholamine at a concentration of 10^-4 g/ml at which musk itself has no action on the papillary muscle. This activity of musk was also proved with tracheal smooth muscle but it had no effect on the action of noradrenaline on vascular smooth muscle. The action of musk does not inhibit the tyramine action, as does cocaine, and there is no change in its action on reserpinized muscle. On the other hand, it inhibits electrical stimulation of the nerves in the hypogastric nerve-vas deferens smooth muscle system. It showed different behavior from cocaine against external noradrenaline and there was no direct effect on it. From these facts, it was assumed that the effect of musk in increasing the action of catecholamine is due to direct participation in β-adrenergic receptor.