Groups (18) of rats were maintained from 30 to 86 days of age on diets containing 18 and 90% casein supplemented with necessary vitamins, 14 groups being subjected to right unilateral nephrectomy at the beginning of the experiment (30 days of age). Histological examination revealed no pathological renal lesions. Renal enlargement due to the high-protein ration occurred in intact rats as well as in those having one kidney. This increase in the size of the kidneys was neither lessened nor prevented by the use of any amt. or combination of vitamins B, G and undifferentiated B employed.