Two types of cold exposures were carried out in humans. A. Fourteen subjects were exposed 4-7 times within 2 weeks to the following conditions: ambient temperature was decreased from 28 degrees C to between plus and minus 5 degrees C; the subjects wore a bathing suit and remained in a resting position during the exposure which lasted for 1h. B. Nine conscripts were studied before and after a 10-day exercise, during which they were exposed to moderately cold conditions during day and night. The exercise did not require increased physical activity. In two thirds of the subjects A, metabolic reactions and shivering threshold were shifted to a lower weighted mean body temperature as well as a lower esophageal temperature ("hypothermic" type of adaptation). This modification in the thermoregulatory system was linked with a reduction in thermal discomfort and cold sensation. No change was found in the resting metabolic rate nor was there any indication of the development of non-shivering thermogenesis. Similar modifications were found in 4 of the 9 soldiers (study B). These 4, however, had particularly high shivering thresholds before the 10-day exercise and the values found thereafter were no lower than those found in the remaining five and in the subjects of group A before the cold-exposure regimen.