Two different paradigms have been used to assess auditory gating in human subjects, namely prepulse inhibition (PPI) of the acoustic startle response (ASR or sensorimotor gating) and gating of auditory evoked potentials (AEPs or sensory gating). PPI is the reduction in the ASR that occurs when a weak stimulus (prepulse) precedes a startling stimulus with interstimulus intervals between 30 and 500 ms. PPI has been found to be disturbed in schizophrenic patients. In the sensory gating paradigm, an auditory click (S1) is presented to a subject, eliciting a positive deflection at 50 ms after stimulus onset in the electroencephalogram (EEG). This deflection is referred to as the P50 component. After a brief interval, about 500 ms, a second click (S2) elicits a much smaller P50 in normal control subjects, who are said to show normal gating. The reduction in P50 amplitude to the second click has been found to be less pronounced in schizophrenic subjects. This review discusses the similarities and differences between the AEP gating and PPI paradigms. Emphasis in the discussion is placed on the role of dopamine. Growing evidence from both human an animal studies supports the suggestion that AEP gating and PPI underlie different inhibitory systems. Therefore, it is concluded that PPI and AEP gating have neural substrates that only partly overlap each other and that both paradigms measure distinct types of gating mechanisms.