The risks are assessed of African labourers developing heat-stroke levels of body temperature, i. e. a mouth temperature of 105 ° F, while working moderately hard in a saturated air temperature of 92 ° F and an average wind velocity of 450 ft/min on thefirst day after the Chamber of Mines two-stage method of acclimatization (12 days) and after an abbreviated form comprising 3 days in cool and 3 days in hot air conditions.