Visually and auditory evoked EEG potentials were studied in 248 healthy university students, who were carriers of one of the following hereditary EEG variants: Monomorphic alpha-waves; low-voltage-EEG; EEG in which the alpha-rhythm was mixed diffusely with beta-waves; and EEG with fronto-precentral beta-groups. The study uncovered consistent and statistically significant group differences between the EEG-countertypes, monomorphic alpha-waves and the low-voltage EEG: subjects with monomorphic alpha-waves showed higher amplitudes and longer latencies of most peaks of the visually evoked potential (VEP), and higher amplitudes for most peaks of the auditory evoked potentials (AEP). Similar differences between EEG types were shown for two measures--overall amplitude (oscillation) and average latency--of all peaks for VEPs and AEPs. The results are consistent with a hypothesis discussed in an earlier paper in which differences between these two EEG types in processing of information in the CNS were assumed on the basis of psychological test results and neurophysiological theory. The two EEG types with beta-waves in addition to alpha-waves showed latencies of evoked potentials in-between those found in the EEG types with monomorphic alpha-waves, on the one hand, and the low-voltage EEG on the other. There was no significant difference in the frequency of VEP augmenters and reducers between EEG types.