Troxonium tosylate is a triethylcholine ester which resembles hemicholinium in some of its pharmacological effects. In animal pharmacological studies, it was noted that troxonium tosylate had a marked antitremorine activity with an associated hypotensive effect. This antitremorine activity, which is a common characteristic of antiparkinsonian agents, was found to be combined with an inhibitory function on acetylcholine synthesis and with a reduction of brain catecholamines. Troxonium tosylate was found to be an effective antiparkinsonian medication for drug-induced extrapyramidal manifestations. Troxonium tosylate caused a pronounced fall in the blood pressure in both normotensive and hypertensive animals. It produced this depressor effect mainly by antagonism of both central and peripheral autonomic ganglia. Troxonium did not possess atropine-like properties and was not active as an adrenergic blocker. Despite the potent effect upon the blood pressure, it did not significantly inhibit renal function and cardiac output. Because of its unique properties, it was postulated that troxonium might be of value in the management of hypertension of various etiologies.