Nine winter swimmer men were exposed to: (A) sauna and ice water immersion; (B) sauna and 15 degrees C shower; (C) sauna and room temperature; (D) head-out ice-water immersion and room temperature. The exposures were repeated and ended with a recumbent recovery. The initial, post-exposure and post-recovery concentrations of plasma ACTH, serum cortisol, serum melatonin, plasma norepinephrine and plasma epinephrine were determined. ACTH and cortisol indicated a slightly increased post-exposure level. Melatonin concentration did not change. Post-exposure norepinephrine levels increased (P less than 0.05) from the initial. Post-exposure epinephrine indicated a tendency to elevated levels with a nearly doubled (P less than 0.05) concentration in experiment A. The tendency toward enhanced ACTH and cortisol secretion and sympathetic activity shown by increased catecholamine secretion suggest that the winter swimming practice may raise the pain threshold and develop a potential for improved cold tolerance, possibly by nonshivering thermogenesis.