Event-related potentials (ERP) constitute an heterogeneous group of brain electrical signals time-locked to sensory stimulation, motor responses, and associative processes, recorded using computer averaging. Several kinds of brain electrical activity are encompassed by the generic term "event related potentials": sensory evoked potentials, time-coherent cerebral events related to motor acta, long-latency potentials associated with psychological variables, slow potential shifts linked to psychological constructs, and "emitted" cerebral events of endogenous origin. Shortcomings of this classification are pointed out and a simpler one is proposed, distinguishing between sensory, motor, and associative time-locked potentials. Their clinical use is illustrated under six major headings: testing of sensory function, localization of lesions, maturation of the central nervous system, genetic markers, evaluation of pharmacologic agents, and indicators of cognitive processes, borne methodological issues relevant to the clinical use of ERP are discussed.