In order to assess whether the fluctuations in the sweating response occurring during sleep are related to changes in central drive or in peripheral sweat gland reactivity, 4 healthy male subjects spent 6 non-consecutive nights in a climatic chamber. Air temperature was 25 degrees C, dew-point temperature was 10 degrees C and air velocity was 0.3 m X s-1, while wall temperature was either 38 degrees C, 46 degrees C or 48.7 degrees C giving 3 levels of operative temperature (To = 30, 33 or 34 degrees C). During the whole night, 2 local sweating rates on the right and the left sides of the upper chest were continuously recorded from 12 cm2 area capsules using a dew-point hygrometer technique, while applying local thermal clamps, a constant 2 degrees C difference in local skin temperatures being imposed between the two symmetrical skin areas. Continuous measurements were made of rectal temperature, 10 local skin temperatures, 2 EEGs, 2 EOGs, 1 EMG and 1 ECG. Results show that the multiplicative relationship between the peripheral influence of local skin temperature and the central drive for sweating described in waking subjects, is still valid in sleeping subjects. No peripheral change appears in sweat gland reactivity between the different sleep stages. Changes in the sensitivity of the thermoregulatory system occurring during sleep cannot be explained by a local factor acting at the sweat gland level.