The differences in the waveform of Cerebral EP (Evoked Potential)s; SEP, VEP and AEP, among healthy subjects, schizophrenics, manic-depressives and epileptics were investigated. In 585 subjects of both sexes comprising these diagnostic groups, 6 channels of EPs, each 2 channels for each sensory modality, were recorded simultaneously/parallelly from each subject, without assigning a mental task. Then, waveforms of the g-m (group mean) EPs of each diagnostic group were superimposed for inspection. Peak latencies and inter-peak amplitudes of individual EPs were statistically tested among (ANCOVA) and between (Scheffe's multiple comparison test) these diagnostic groups for each channel (modality), and for each sex. The waveforms of g-m EPs of each diagnostic group differed from each other. The differences of latencies and inter-peak amplitudes among these diagnostic groups attained to the significant level (P<0.05), with more significant differences between healthy subjects and each of these pathological diagnostic groups than between each of these pathological diagnostic groups, for each sex. Thus the differences in the waveform of EPs among these diagnostic groups were confirmed even taking the effect of medication on EPs into consideration. These results might suggest the existence of a waveform for individual EPs specific to each of these diagnostic groups, for each sex.