Auditory event-related potentials (ERPs) to pure tones and performance on a measure of item recognition were compared in 20 controls, 14 alcoholics, 20 depressed and 21 schizophrenic patients. Compared with normal controls, P2 and N2 were delayed and of diminished amplitude in the psychopathological groups. Increased amplitude of P1 in alcoholics, diminished N1 in depressed patients, increased latencies of N1 in schizophrenics and N2 in alcoholics were pathology-specific. Unusual patterns of response in the item recognition test (elevated intercept and flattened slope) and its relationship with ERPs distinguished the diagnostic groups from the controls. Support for the preferential involvement of the left hemisphere in schizophrenia and of the right hemisphere in depression was found. Disinhibition of CNS activity in the response of alcoholics (increased P1 and delayed P3) was indicated. The findings suggested that discriminant analysis of auditory ERPs to simple, pure tones, in conjunction with psychometric data significantly differentiated pathologic groups from each other and from controls.