The peripheral (tail) circulatory responses of six male albino rats were measured at ambient temperatures between 5 and 40 degrees C, using impedance plethysmography. Each animal was anesthetized, instrumented, and placed in a thermal environmental chamber to reach equilibrium. Tail blood flow, respiration rate, heart rate, core temperature, and tail skin temperature were then monitored at each ambient temperature. The mean tail blood flow was significantly higher (p less than 0.05) at 5 degrees C than at 10 degrees C. The mean blood flow increased significantly (p less than 0.01) at each of the temperatures above 10 degrees C. Tail skin temperature and internal body (core) temperature increased significantly with increasing ambient temperature.