The aim of this study is to investigate the relation between the fall in forearm skin temperature and the rise in rectal temperature during exercise in the process of heat acclimation. Trained 3 males served as subjects. One day experiment contains both 75W exercise intensity for 10 min control exercise under the ambient temperature (Ta) of 28°C, relative humidity (r.h.) of 40% and for 30 min acclimation exercise.
　During 10 min control exercise, the environmental conditions and work intensity were set so that changes in skin temperature could be observed without the interference of sweating.
　Acclimation exercise were initial neutral control (INC) 3 days under the Ta; 28°C, r.h.; 40%, heat environment (HE) 10 days under the Ta; 50°C, r.h.; 40%, and final neutral control (FNC) 3 days under the Ta; 28°C, r.h.; 40%.
　The final rectal temperature decreased progressively in the HE 2nd to 8th days. On the other hand, the final forearm skin temperature increased progressively in the HE 5th to 10th days. In the HE 5th to 8th days, the final rectal temperature was negatively correlated to the final forearm skin temperature.
　These findings suggest that the rise in core temperature during exercise results from the decreased dry heat loss due to a fall in skin temperature.

DESCENTE SPORTS SCIENCE Vol.10/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE