A clinical application of the property of anticholinesterase drugs to prolong the action of suxamethonium is described. A trial has been conducted using the anticholinesterase tetrahydroaminacrine (THA) in association with suxamethonium to provide muscle relaxation during 1,470 surgical operations. The technique involves the intermittent injection of small doses of suxamethonium (10 mg cation) following an initial priming dose of both THA and the muscle relaxant. The average consumption of suxamethonium is 75 mg cation per hour. The method facilitates the maintenance of an even degree of relaxation in response to intermittent injections of suxamethonium. Prolonged neuromuscular block is a hazard if the recommended scales of dosage be exceeded.