Present data on 60 comatose patients with head trauma, hypoxia and cerebrovascular disease suggested that SER may yield quantitative, useful information concerning the functional state of the cerebral cortex. To assess the prognosis of individual patients we propose to classify patients from various etiologies of coma into the following categories: I. If there is bilateral absence of cortical responses, irrespective of the etiology of coma, none of these patients recover. II. If the initial cortical responses in the first 24 hours are normal, then it is imperative that these should be repeated in the first week before any definitive prognosis can be given, (since as in one case, we noted on the fifth day there was distortion of amplitude of his response and eventually the cortical responses were unobtainable, therefore indicating a poor prognosis). III. Patients who have normal responses throughout the acute course of illness carry an excellent prognosis from coma of all etiologies, except with ischemic etiology. The prognosis remains favorable for recovery from coma, but these patients may remain with significant neurological deficits. IV. When there is a 75% drop in the amplitude of the responses, it indicates a poor prognosis for ultimate neurological recovery, and the majority of these patients will remain in a persistent vegetative state. V. In patients with intermediate reduction in amplitude, 25-50% carried a moderate prognosis, and the majority of these cases in our series were able to perform activities of daily living.