Alpha EEG reactivity was assessed in a carefully diagnosed sample of 84 schizophrenic and schizophrenic spectrum disorder patients, both under resting conditions (eyes closed and eyes open) and during two spatial-geometric cognitive tasks. The influence of the subject's demographic (sex and age), clinical (diagnostic subtypes, disease course, CT scan characteristics) and neurophysiological (hemispheric recording and different cognitive tasks) characteristics on alpha peak reactivity was analyzed by means of multivariate analysis of variance. The results indicated a significant effect of type of illness on alpha EEG reactivity, patients with a diagnosis of undifferentiated and disorganized schizophrenia having the lowest alpha reactivity levels. None of the other variables considered had any contributing effect. The results are discussed in terms of orienting responses and hemispheric CNS organization in functional psychoses.