Test batteries for assessing psychological function following toxic exposure should evaluate sensory processes. Sensory function has intrinsic importance as an endpoint measure, and because performance in other behavioral tests typically requires that the organism can detect significant environmental events, its evaluation is necessary to the proper interpretation of other tests. In addition, the psychological and physiological principles concerning sensory function are relatively well known, as is the comparative structure of the sensory systems across species. This knowledge provides the necessary empirical and theoretical base for extrapolating sensory effects of toxic exposure across species. An analysis of sensory function is described that uses the demonstration of reflex inhibition by irrelevant stimuli as an objective measure of stimulus detection. Two basic parameters of reflex inhibition in several species are detailed, its sensitivity to near threshold stimuli is discussed, and the effects of sensory dysfunction on reflex inhibition are demonstrated. This method has much to recommend it for toxicology, including its rapidity, its objectivity, its sensitivity, and its suitability for use in both humans and a variety of laboratory animals.