Thyroid hormone responses to prolonged cold exposure in man

1. Four men, of ages varying from 23 to 28 years, living at Halley Bay, Antarctica (75° 31′ S, 26° 39′ W), were exposed to a mean air temperature of 6·6° C. 2. The concentration of serum triiodothyronine (T3) 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 (T4) rose more slowly than did the T3, 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.