Currently, there are two main hypotheses explaining the autistic syndrome, concerning the sensory and cognitive information processing levels in the central nervous system (CNS). One possibility is that the autistic patients have a disturbance of the subcortical brain-stem sensory processing, and the other is that information processing at the higher cortical cognitive level is impaired. Brain-stem evoked potential (BEP) , middle latency evoked potential (MLEP) and event related potential (ERP) techniques could be clinically useful for the evaluation of the subcortical brain-stem function, and the cortical function. This research investigated the neurophysiological mechanisms of the processing of sensory input in 9 normal (control) and 9 autistic children, using the technique of brain-stem auditory evoked potentials (BAEPs) to gauge neural activity to click auditory stimuli. In the earliest components which occur in the 10 msec range, the wave I represents activity in the auditory nerve, and the remaining waves represent synaptic transmission upwards through the ipsilateral and contralateral lemniscal pathways. In this experiment, only 2 of 9 autistic subjects showed BAEP abnormalities, but the other autistic subjects did not show any difference as compared to the controls. If BAEP abnormalities were found, they mignt be related to organic neurological disorders. It is known that the P3b component is small in autistic children. But, some autistic subjects have deviant BAEPs, and they also have deviant middle latency auditory evoked potentials (MLAEPs). Such a neurophysiological investigation by evoked potentials (EPs) may be a clue to the understanding of a subtype of the autistic syndrome.