In order to investigate the seasonal difference in physiological responses to heat, nine young Japanese males were exposed in supine position to the hot environment at 50°C with 50% relative humidity for 61 minutes in July (summer) and December (winter) . Rectal temperature at 28°C prior to heat exposure was significantly higher in summer than in winter. During heat exposure, rectal and mean skin tempeartures were significantly higher in summer than in winter, but their increase rates did not show significant differences between summer and winter. It was considered that seasonal differences of rectal and mean skin temperatures during heat exposure were due to their seasonal differences before exposure. It was concluded that basic physiological state induced by seasonal acclimatization may have important roles in physiological response to heat and heat tolerance of man.
