Metabolic rate (M), mean skin temperature (Tsk) and rectal temperature (Tre) were studied during 2 h exposure to cold in the air (Ta = 15-25 degrees C) and in water (TH2O = 24-32 degrees C). From the results, it was possible to draw tentative equations of the metabolic response in transient and steady state as functions of body temperatures: Mair = 41,3-57.77 dTsk/dt-5.01 (Tskt-Tsk0) and Mwater = Mair + 984.15-23.79 Tre. These equations show an important difference between the two groups of experiments: in water, both Tsk and Tre are required, whereas Tsk suffices in air. This leads to discuss the usage of mean weighted skin temperature and rectal temperature to describe peripheral and central input respectively, specially on man in cold air, in the range of these experiments.