A description is given of an audiovisual reaction time task, performance of which was maximal after 15 min. practice and which lasted at this level for 1 wk. Sensitivity of the test was shown in an adverse effect of inhalation of traces of anesthetic gases. Comparing responses to auditory and visual stimuli, the control auditory reaction times were faster but were lengthened more in the presence of anesthetics than were the visual ones. This test may be useful in other studies of subtle depressant drug effects.