A study has been conducted on goats to determine whether thyroxine injd. subcut. is excreted in the feces and/or urine in a biologically active form. Unmistakable activity appeared in the feces of goats during the 5th through the 10th day of a 10-day injn. period. Estimations of active material in the feces are presented in terms of the amt. of disodium thyroxine required to evoke an equivalent response. No activity could be detected in normal goat feces or urine, in feces collected during the first 5 days of injns., or in urine collected at any time during the injn. period. Various possible mechanisms of thyroxine inactivation are discussed.