Daily injs. of alkaline extract of beef ant. pituitary (Evans'' growth hormone prep.) into 22 [female] rats over a period of 6 mos. stimulated growth. This growth was slightly hypergonic for the skin and liver, and significantly so for the heart. The thyroid glands of the injected rats were relatively smaller and their adrenal glands absolutely smaller than those of the controls. The B.M.R. (127 4-hr. dets. on injected rats and 118 on controls) of the injected rats per unit wt. and even per unit surface was consistently and significantly lower than that of the controls, both during the period of injs. and after their cessation. These differences between the giant rats and normal littermates could evidently not be explained by genetic differences or by changes in the water or protein content of the rats. The in vitro rate of O2 consumption per unit of dry wt. of tissue (diaphragm) was smaller in the injected rats than in the controls, indicating a residual effect of the previous condition of the animal. These results were regarded as an example of somatic adaptation of tissue metabolism in vivo as well as in vitro to a condition of the animal as a whole, particularly to its endocrine system, which was in correlation to body size.