This study was performed to determine the effect of body heating prior to extreme cooling. Subjects were heated in a 42° C water bath until heart rates reached 150 beats/minute or rectal temperatures reached 39. 5° C. Subjects were exposed, following heating, to ambient air temperatures of 0° C for 30 minutes and -15° C for 60 minutes. No significant change in tolerance times was noted. Total body heating prior to exposure is an ineffective means of extending the human body's tolerance to extreme cold. A discussion of the results is presented.