Functional imaging technique using positron emission tomography (PET) has made it possible to localize functional brain regions in the human brain by detecting changes in regional cerebral blood flow (rCBF). Performing PET studies in the monkey will aid in integrating monkey electrophysiological research with human PET studies. We examined changes in rCBF during olfactory or combined olfactory and gustatory (flavour) stimulation using PET in the alert rhesus monkey. Olfactory or flavour stimulation with acetic acid or apple increased rCBF in the prepyriform area, substantia innominata and amygdala. Besides these areas, flavour stimulation increased rCBF in the anterior insula and frontal operculum, orbitofrontal cortex, inferior frontal gyrus and cerebellum. Apple odour or flavour stimuli increased rCBF in the inferior occipital gyrus in addition to the above areas. These findings suggest that the increases of rCBF in response to neural activities in the primary olfactory and gustatory cortices are detectable by the use of PET. In addition, regions activated by apple stimuli suggest that higher brain function might be detected with PET in the alert monkey.