As reflected by increasing plasma concentrations of cortisol, norepinephrine, epinephrine and dopamine, a marked stimulation of the adrenal cortex and of the sympathetic nervous system occurred in Syrian hamsters during moderate hypothermia induced by helium-oxygen atmosphere and cold. 2. A profound hyperglycemia was observed during hypothermia. 3. All effects due to the helium-oxygen atmosphere and cold exposure (helox-cold) disappeared almost completely after rewarming. 4. The results corroborate the hypothesis of an involvement of the adrenal cortex combined with the sympathetic nervous system in the control of acute induced heat production.