OBJECTIVE The purpose of this study was to determine the effect of 12 degrees C cold exposure for 180-minutes on the hormonal responses of sleep-deprived individuals. METHODS Participants underwent 2 cold-air trials: 1 after a normal night of sleep (ie, 6-8 hours) and 1 after 33 hours of sleep deprivation (SDEP). A venous blood sample was taken at baseline and then at 90-and 180-minute cold-exposure time points. Repeated-measures analysis of variance was used to determine significance between a normal night of sleep and SDEP for norepinephrine, epinephrine, cortisol, insulin, thyroid hormones triiodothyronine and thyroxine, glucose, and non-esterifled fatty acids. RESULTS There was no significant main effect for time, trial, or interaction for insulin, thyroid hormones, epinephrine, cortisol, and glucose (P < or = .05). A significant main effect for time for norepinephrine and non-esterified fatty acids was demonstrated (P < .001). CONCLUSIONS The lack of significant differences in the hormonal and metabolic responses to cold exposure combined with SDEP may have been because of an ability of the individual to continue to respond despite the environmental stressor or the physiological effect elicited from cold exposure, thereby possibly masking physiological responses of SDEP. CONCLUSIONS On the basis of these data, SDEP combined with protracted cold exposure apparently was not a great enough stressor to cause a differential response in the hormonal and metabolic parameters.