The relation of the hippocampal EEG to behavior and to the neocortical EEG is being studied in psychomotor epileptics. Hippocampal recordings displaying only rare epileptiform spikes and slow waves are found to follow grossly the simultaneously recorded neocortical EEG, becoming desynchronized during wakefulness and paradoxical sleep (PS), and displaying large irregular slow waves during slow-wave sleep. In the one patient reported in this clinical note, strong rhythmic 5--6 c/sec waves dominated the neocortical and hippocampal EEG during quiet wakefulness. These slow waves were replaced by desynchronized activity during PS and during difficult tasks, suggesting a further desynchronizing influence. The findings in all patients suggest that the rhythmic slow activity ('theta') found in rats and cats during specific behaviors is not observed in the human hippocampal formation during the homologous behaviors.