To compare the thermoregulatory responses of normal subjects and patients with atopic dermatitis, the effect of exercise under moderate heat stress was examined in two groups of subjects. Each group of eight subjects (controls or clinical atopics) underwent a 90-min experiment after being equipped with probes for measurement of core and skin temperatures, heart rate and overall and local sweating rates. Sweat surface tension was determined from sweat collection made at the end of the session. The experimental procedure was as follows: 30 min rest at thermoneutrality, 30 min cycling at 90 W at 36 ~ followed by 30 min recovery sitting at rest at 36 ~ on the cycloergometer. None of the registered variables differed significantly between the normal and atopic subjects except for variations in mean skin temperature, core-to-skin temperature difference and sweat surface tension. Since local sweating on non-affected skin under a controlled thermal clamp was not altered by atopy, it can be concluded that the thermoregulatory modifications under heat stress is of vasomotor origin, the benefit of which, in terms of heat dissipation capacity, remains uncertain. There may be alterations in the constituents of sweat, but not in its excretion rate. Local, rather than central, factors are probably involved in this qualitative change, which remains to be investigated.