Thyroid hormone response to prolonged cold exposure in man.

1. Four men, of ages varying from 23 to 28 years, living at Halley Bay, Antarctica (75 degrees 31' S, 26 degrees 39' W), were exposed to a mean air temperature of 6.6 degrees C.2. The concentration of serum triiodothyronine (T(3)) rose significantly by the second day, remained raised, and returned to pre-exposure levels within 2 days of return to a normal environment.3. The concentration of serum thyroxine (T(4)) rose more slowly than did the T(3), reaching a maximum in 3-4 days and also returning to normal within 2 days of return to a normal environment.4. There was a wide individual variation in the change of concentration of serum cortisol.