Eighteen myasthenic patients have been operated on under general anaesthesia; 14 subjected to thymectomy and 2 to emergency procedures (caesarean section and laparotomy because of intestinal obstruction). Atracurium (0.3 mg/kg) and vecuronium (0.06 mg/kg) exhibited a long duration of action only in the two cases affected by the more severe signs and symptoms of the disease.