7 young men marched for 6 days (35 km daily) in a cool climate at about 35% of their VO2max. Sweat output was measured at rest in a climatic chamber during a controlled hyperthemia test performed before and after the trial. 4 subjects served as controls. The main finding of the study was that sweat output increased 17.3% +/- 1.5 SEM on the post-trial test, without any change in VO2max. It is concluded that moderate physical training can improve heat responses in resting man.