We used positron emission tomography to evaluate differential processing of olfactory, gustatory and combined olfactory and gustatory (flavor) stimuli as indicated by comparison of evoked cerebral blood flow (CBF) changes during these conditions. We found significant CBF decreases in primary gustatory and secondary gustatory and olfactory cortices during simultaneous presentation compared with independent presentations of identical stimuli, suggesting that flavor processing is not represented by a simple convergence of its component senses. Additionally, CBF increases in the amygdala and basal forebrain were observed in a mismatched flavor condition versus a matched flavor condition, suggesting a role for these structures in processing novel or unpleasant stimuli.