In comparison to other senses, the electrophysiology of olfaction has been little studied in man and some of the basic paradigms used in the study of the other senses have not yet been widely applied to its study. Basic information such as the effect of stimuli of different intensities on the olfactory evoked potential (OEP) has yet to be presented. To this end, 12 subjects received olfactometrically delivered odorant pulses of toluene at three intensity levels-- 1,600, 8,000, and 16,000 ppm. Data were obtained from three electrode sites, Fz, Cz, and Pz. An ANOVA revealed significant stimulus intensity and site effects. There was no difference in amplitude at the lowest intensities but there was a significant increase in amplitude evoked by the 16,000 ppm stimulus. The amplitudes recorded from Fz differed from those recorded from Pz. No latency differences were found, although there was a trend toward briefer latency with greater stimulus concentration. The OEP responds with increased amplitude to increased stimulus intensity as do evoked responses in other sensory modalities. Stimulus control over the OEP amplitude can be obtained by varying the stimulus intensity. These data are evidence that the common principles of sensory processing can be extended to include the sense of smell.