There is considerable uncertainty regarding the cortical areas in the human brain that are involved in gustatory processing. Evidence from nonhuman primates indicates that parts of the peri-central opercular region (secondary somatosensory cortex) and insular cortex may be important for gustatory processing. The aim of the study was to examine changes in cerebral blood flow during gustatory stimulation (with sucrose or water) in the insulo-opercular region of the human brain with positron emission tomography using only movement of the tongue and mouth as control conditions. This is important because subtractions of responses to one gustatory stimulus from those to another may mask gustatory activity that is common to both stimuli, even when the control stimulus is an apparently tasteless one (e.g. water). Bilateral increases in activity were observed in the insulo-opercular region and, consistent with animal work, they indicate that there are a number of separate foci within this general area where primary gustatory inputs may be processed.