Six patients with the syndrome of "painful legs and moving toes" were studied. Although clinical differences were nonspecific, the EMG disclosed two subgroups: one with a simple, erratic pattern of spontaneous activities in foot and leg muscles, and the other with a complex alternating pattern in antagonistic muscles. In the first group, the physiopathologic mechanism is thought to act in the periphery: in the lumbar roots when local anesthesia of the posterior tibial nerve suppresses spontaneous discharges, or in the nerve trunk when it is ineffective. In the second group, the symptomatology may be generated centrally, implying a more general disturbance of sensorimotor control.