A patient with continuous muscle fiber activity is described. From our search of the literature, we believe this is the oldest patient with a reported case of this disorder, and the symptoms and treatment varied from previously reported cases in these respects: symptoms remained confined to the lower extremities after 18 months had elapsed, there was no response to phenytoin sodium or carbamazepine, and the patient required a full dose of tubocurarine chloride to stop the abnormal myoelectric potentials. A site of dysfunction in the unbranched motor axon is suggested as the locus of generation of the stimulus for the abnormal myoelectric activity.