To elucidate brain dysfunction in patients with methamphetamine psychosis, we examined background EEG activities by means of the frequency analysis, P300 of auditory event-related potentials and the auditory brainstem evoked response (ABR) in 17 patients and 35 normal controls. The patients were divided into two subgroups according to their symptomatology in the acute stage of psychosis : the hallucination-delusion group of 10 patients who had experienced paranoid delusions and hallucinations and the psychomotor excitement group of 7 patients who had exhibited a severe catatonia-like excitement but had never experienced hallucinations or delusions. Abnormalities found in the patients were as follows : 1) The total powers were decreased in δ, θ and α2 frequency bands ; the decrease was most prominent in the α2 band and more pronounced in the psychomotor excitement group. 2) P300 amplitudes were decreased ; the decrease was found only in the hallucination-delusion group. 3) ABR latencies were increased, particularly for wave V and waves V-I inter-peak interval ; the delay was more marked in the hallucination-delusion group. The findings suggest that the cortical dysfunction is mainly involved in the psychomotor excitement group, while the subcortical dysfunction in the hallucination-delusion group.