Abstract
1. Pellets of L-thyroxine (30 mg.) were implanted subcutaneously in sheep. The loss in weight of the implants and the plasma P.b.i. level were determined at intervals.2. The P.b.i. concentration increased within a few days from a normal value of around 5 μg./100 ml. to one of 15–20 μg./100 ml. After 10–20 days the concentration slowly returned to normal, and at 70 days subsequent to implantation was only slightly above the normal level.