This study evaluated the effect of temperature on blood flow by using rubidium 86 to determine the fraction of cardiac output going to specific facial tissues of rats. Seventy-seven male Holtzman rats were divided into two groups and various subgroups. The intraoral subgroups were categorized according to the temperature of the water irrigating the oral cavity (11 degrees, 39 degrees, 41 degrees, 43 degrees, or 45 degrees C). The extraoral subgroups were categorized according to whether heat or ice was applied to the cheek of the rats and the duration of application (10 or 20 minutes). Rats were killed within 60 seconds after injection of 86Rb, and tissue samples were taken from the buccal mucosa, facial skin, masseter muscle, mandible, tongue, and maxilla. The fraction of isotope uptake in each gram of these tissues (FU/g) was then calculated. For the intraoral group, the bath temperature of 39 degrees C increased the FU/g in all tissues except masseter muscle and tongue. Higher bath temperature did not further alter the FU/g. Lowering the temperature to 11 degrees C changed the FU/g significantly only in the tongue. For the extraoral group, 20-minute application of ice was required to reduce FU/g significantly in all tissues but masseter muscle and skin. Extraoral heat application for 10 minutes increased FU/g significantly in skin and tongue, but no further change was seen after 20 minutes of application.