A soft prepulse just before a loud noise attenuates the normally expected startle reaction(prepulse-inhibition, PPI, sensorimotor gating): a click just before a second one interferes with some of the ERP components normally elicited by the second click (sensory gating). Here we examine the similar gating effects to be expected when a prepulse precedes two tones presented ina Go/no-go discrimination. Methods: Nine young patients with schizophrenia were compared with 11 healthy subjects (mean 23y). Prepulses (50 dB) were presented 100 or 500 ms before the 65 dB 800 or 1400 Hz tones. The CNV and eye-muscle responses were monitored in addition to the P50 and P300 event-related potentials. Results: 1/ In normal subjects prepulses at the 100 ms interval interfered with the eye-startle response. This reduction correlated with that for the P300. 2/ The patients showed a reduced CNV, less P50 conditioning, and less gating of the eye-startle response. Conclusions: Clearly sensory gating is relevant for information processing leading to the formation of appropriate behavioural responses. Part of this system appears to be deficient in young patients with schizophrenia.