• We analyzed the EEGs of 27 schizophrenic patients and 132 patients with affective disorder who received diagnoses according to rigorous research criteria. The proportion of abnormal EEGs was twice as great among schizophrenics as among affectives, and when the groups were compared for localized cortical differences, schizophrenics had more temporal abnormalities and affectives more parieto/occipital abnormalities. There was also a trend toward different hemispheric ateralization for the two groups, with a reversal of the relative proportions of left- and right-sided abnormalities. These differences were unrelated to age, sex, severity of illness, or past or present drug administration. These findings are complementary to those of other workers, lend support to the validity of our diagnostic research criteria, and provide additional evidence for neurophysiological differences between schizophrenics and patients with affective disorder.