Cinnamaldehyde increased contractile force and beating rate of the isolated perfused heart of guinea pigs. These effects were antagonized by propranolol and virtually abolished by reserpinization. Cinnamaldehyde released catecholamines from the isolated adrenal gland of dogs, whereas cinnamyl alcohol and cinnamic acid were devoid of such effect. Benzaldehyde also released catecholamines in the same preparation but its potency was lower than that of cinnamaldehyde. Cinnamaldehyde released catecholamines from the adrenals of pentobarbitalanesthetized and splanchnicotomized dogs by its close i.a. application to the organ, which was confirmed by measuring catecholamine contents in adrenal venous blood. Blood pressure in the same in situ preparation was raised by i.a. application of cinnamaldehyde and this pressor response was antagonized by phentolamine but not by combination of hexamethonium and atropine. When adrenal venous blood was taken out from the circulation immediately after an i.a. application of cinnamaldehyde, the pressor response was not observed in most cases. In conclusion, cinnamaldehyde released catecholamines from the adrenal gland of dogs through a direct action (independent of cholinergic receptor sites) on the organ, cinnamaldehyde was presumed to elicit positive ino-and chronotropic actions on the heart of guinea pigs by releasing endogenous catecholamines, and the aldehyde group in cinnamaldehyde molecule played a role in its catecholamine releasing effect from the organs.