Three patients with infantile neuroaxonal dystrophy (INAD, Seitelberger's disease) studied between ages 2 and 5 years, with the characteristic electroencephalographic pattern of high-voltage, fast (16-24 c/sec) rhythms and absence of reactivity on eye-opening or closure (Radermecker and Dumon-Radermecker 1972), also showed no changes in response to intermittent photic stimulation and absence of evoked potentials to flashes, clicks or median nerve stimuli. Although some theta rhythms and delta activity appeared during drowsiness and sleep, the fast rhythms persisted as the dominant feature. There were no central transients or K-complexes. When the patients cried, with hyperventilation, and also during breath-holding spells, slow rhythms appeared and the fast rhythm was reduced. These findings are interpreted as evidence of cerebral cortex isolation, the fast rhythm representing the spontaneous ("idling") activity of the cortex largely disconnected from subcortical or remote cortical influences by the slowly progressive, selective degeneration of axons, characteristic of the pathology of INAD, but the cortex remains responsive to chemical influences. These electrophysiological features become established furing the third year of age, prior EEGs being normal and later ones showing paroxysmal and other abnormal features in addition to the fast rhythm.