OBJECTIVE: Because many schizophrenic patients are heavy smokers, it has been suggested that nicotine normalizes some neuronal deficit involved in their illness. Schizophrenic subjects have various difficulties with maintenance of attention and selective processing of sensory information. One defect in sensory gating in schizophrenia has been characterized by recording auditory evoked potentials. Most normal subjects have a decrease in the evoked response to the second of two closely paired stimuli, whereas most schizophrenic subjects do not. The aim of this study was to determine whether smoking normalizes this deficit in auditory sensory gating in schizophrenia. METHOD: Changes in auditory sensory gating in response to smoking cigarettes were studied in 10 smokers without psychiatric illness and 10 schizophrenic smokers. Both groups were asked to abstain from smoking from 11:00 p.m. until 8:00 a.m. the next morning, when their auditory evoked responses to pairs of clicks were recorded. The ability to gate sensory information is reflected in a decrease in the P50 wave amplitude in response to the second of the two stimuli. After baseline recordings, the subjects smoked as much as they wished, and then two postsmoking recordings were performed. RESULTS: The schizophrenic patients had a marked but brief improvement in P50 auditory gating immediately after smoking, whereas P50 gating for the normal smokers was slightly impaired. CONCLUSIONS: This study suggests that cigarette smoking can transiently normalize the impairment of auditory sensory gating in schizophrenic patients.