Effect of i.v. and i.d. cinnamaldehyde on plasma catecholamine concentration along with intestinal absorption of the drug was studied in anesthetized dogs. Cinnamaldehyde increased plasma catecholamine concentration, the effect produced through i.d. route (50-100 mg/kg) being dose-dependent and more lasting compared with that through i.v. route (20 mg/kg). In the case of 200 mg/kg of i.d. cinnamaldehyde, an exceeding increase in this parameter was obtained during the later period of time course. Intestinal absorption of cinnamaldehyde i.d. administered, which was investigated through measurement of cinnamaldehyde concentration in the portal venous blood and in blood of the postcava, occurred very early and was long-lasting. Increase in plasma catecholamine concentration produced by i.v. cinnamaldehyde disappeared after blood circulation through the adrenal glands was stopped, and was not influenced with pretreatment of hexamethonium plus atropine. Almost all the increased portion of plasma catecholamines by i.v. or i.d. cinnamaldehyde was epinephrine. It was concluded that cinnamaldehyde, entering the circulatory system, reaches the adrenals and releases catecholamines from the organ through a mechanism(s) independent of affecting the cholinergic system. i.v. DMPP which was used as a referential drug also increased plasma catecholamine concentration.