Little data is available on regional blood flow in the normal primate oral mucosa and none on that in atherosclerotic animals. Three adult Rhesus monkeys were maintained on a normal diet and 4 on a high fat, high cholesterol diet for 20 months. Radiolabelled microspheres were used to measure blood flow in skin and 16 oral mucosa regions. In normal animals, blood flow ranged from 160.81 to 8.68 ml/min/100 gm tissue. Blood flow in the same regions of atherosclerotic animals showed significantly lower values than in controls, ranging from 65.90 to 1.04 ml/min/100 gms tissue. However, the relative blood flow to the different regions was not significantly different between control and atherosclerotic animals. Histologic examination of tissue from the atherosclerotic animals revealed gross intimal plaques occluding the lumina of the carotids and atherosclerotic lesions in the lingual arteries. It is concluded that the decrease in blood flow in oral mucosa in the atherosclerotic animals is not the result of local changes in the mucosal vasculature but may be related to lesions seen in the major afferent vessels.