The present study was designed to investigate whether there is a consistent response in ongoing EEG due to repetitive olfactory stimulation. Two odors of different hedonic quality were presented bilaterally to five male subjects at suprathreshold levels. A room-air blank served as the control stimulus. Each odor was presented six times to each subject in each of three sessions. Electrocortical activity, heart rate, skin conductance and breathing cycle were recorded continuously. EEG variables assessed were difference scores of absolute power in the frequency bands theta, alpha1, alpha2 and beta1 at eight locations. Phenylethyl alcohol was rated pleasant, while valeric acid was judged unpleasant. Within 8 s after stimulus release, valeric acid increased alpha2 power, whereas phenylethyl alcohol did not. No further frequency bands were affected by olfactory stimulation. These findings suggest that smelling an unpleasant odor leads to a cortical deactivation. Chem. Senses 20: 505–515, 1995.