A 50% ethanol extract of Coscinium fenestratum stem material (AECF) has been found to possess hypotensive action in anaesthetised dogs, rats and guinea pigs in a dose-related pattern. The fall in blood pressure was not modified by alpha and beta adrenergic blockers, cholinergic and histaminergic antagonists or by ganglion blocking agents. The effect was more pronounced in spinal-transected animals. AECF non-specifically inhibited the pressor responses to epinephrine, norepinephrine, DMPP and depressor responses to acetylcholine and histamine. AECF failed to exhibit any hypotension when administered via cannula into the lateral cerebral ventricle. Given orally to mice, AECF did not exhibit grossly observable central nervous effects up to doses of 800 mg/kg. The oral LD50 was estimated to be 1200 mg/kg in mice.