Myasthenia gravis is an autoimmune disease involving the acetylcholine receptors at neuromuscular junctions.Perioperative management of patients with myasthenia gravis is complicated by their enhanced sensitivity to nondepolarizing neuromuscular blocking agents and their resistance to depolarizing drugs （1）.Prolonged respiratory depression commonly occurs when these agents are used.Atracurium dibesilate is one of a new series of nonde- polarizing agents and is promising by virtue of its rapid degradation by‘Hoffmann elimina- tion’.leaving products with little or no muscle blocking activity.After encouraging results were obtained with atracurium （2-6）

we investigated the neuromuscular blocking effect of different doses of the drug （0.2 mg/kg

0.5 mg/kg） in sixteen myasthenic patients undergoing thymectomy.with continuous monitoring of neuromuscular function.