On the anomalous activity mf thyroxin analogs in tadpoles.

The abnormally high thyroxin-like activity of certain thyroxin analogs is due to the use of the unique test route of immersion. When thyroxin, triiodothyronine, and their propionic and acetic acid analogs are tested by injection into the tadpole, their activities are more comparable to activity levels established in rat and man.