Maximum oxygen consumption for a short exhaustive work (Ex VO2 max) and for a severe cold stress (C VO2 max) were investigated in 8 dogs. Heart rate, plasma catecholamines and substrate concentrations were measured under both conditions. Mean C VO2 max was lower than mean Ex VO2 max. Heart rate and plasma lactate were also lower during cold exposure than during exercise. Average plasma epinephrine concentrations were not significantly different and average plasma norepinephrine concentrations were similar under C VO2 max and Ex VO2 max conditions. A positive correlation was found between plasma lactate and epinephrine concentrations measured under both conditions. It may be assumed that maximum oxygen consumption during muscular exercise is higher than during shivering thermogenesis. This difference does not seem to be due to differences in the involvement of the sympathico-adreno-medullary system.