In this prospective study, five patients who had repeatedly shown troublesome restless emergence agitation after each of 20 sessions of electroconvulsive therapy (ECT) with a succinylcholine dose about .7 mg/kg showed no agitation after 15 ECT sessions in which the succinylcholine dose was increased to about 1.0 mg/kg. The probability that the pattern of response to higher succinylcholine dose resulted from random processes is less than .005. This provides evidence that patients predisposed to emergence agitation are sensitive to seizure-induced metabolic changes in skeletal muscle tissue and that the likelihood of emergence agitation rises with the ratio of skeletal muscle mass to succinylcholine dose. Because ECT-inducted serum lactate elevations are blocked by succinylcholine, emergence agitation might be essentially the same phenomenon as lactate-induced panic.