For this project we initiated a series of experiments to determine if fecal extracts, which are known to contain more or less toxic material, might have any effect upon the thyroid gland when injected intraperitoneally. This paper will be confined entirely to those effects which seem to develop over a relatively long period of time otherwise known as chronic. In this work rabbits were used as experimental animals, not because of their particular fitness to the problem, but because they were the most accessible laboratory animal.