The effects of suxamethonium 1.0 and 0.5 mg/kg were studied in myasthenic patients. Resistance was not encountered at the 1.0 mg/kg dose but was seen at the lower dose. A non-depolarising type of block developed in patients in both groups. However, recovery from the non-depolarising block was not prolonged beyond the requirements of surgery. The neurophysiological basis for, and clinical implications of these findings are discussed.