The basal EEG profile of the aged Fisher-344 rat was consistently different from that of the young rat, showing dominant high voltage slow-wave components. These slow waves were present in both the frontal cerebral cortex and dorsal hippocampus. Absent or greatly attenuated in the aged rat's hippocampal EEG was rhythmic theta activity, which was always dominant in the young awake rat's hippocampus. These EEG differences were clearly apparent only under basal test conditions, i.e., following habituation to the test situation. Pramiracetam sulfate acted strongly to normalize the aged rat's EEG, while the action of piracetam was weak and appeared to undergo tolerance development.