Over the last 70 years the physiological mechanisms responsible for cold adaptation of humans have been studied intensively in several laboratories. However, in spite of this enormous effort, the principle mechanism of cold adaptation in humans has not yet been sufficiently described. Bittel (1987Bittel ( , 1992, when analysing all the data so far obtained, concluded that a hypothermic-insulative type of adaptation predominates. On the other hand, Young et al. (1986) concluded that cold acclimation in humans appears to be primarily of the insulative type. Our recent work demonstrated the existence of a metabolic type of adaptation due to an increased capacity for adrenaline thermogenesis (Lesn a et al. 1999). This paper attempts to clarify differences in the control of the thermoregulatory responses of non-cold-adapted humans and winter swimmers who are able to withstand very low water temperatures. The significance of observed changes in body temperature control and the activity of heat loss mechanisms in the resistance of humans to cold has been estimated. An attempt is also made to quantify the contribution of catecholamine thermogenesis to the total metabolic response to cold and thus to assess the significance of non-shivering thermogenesis in cold adaptation of humans.