1. At all levels of immediate protein consumption, from almost none to excessive amounts, the degree of growth of the single kidney, suprarenal, and ovary left after removal of one of each of these organs is the same up to 5 days after the operation.
2. On a 1 per cent protein diet there is no growth of the remaining organs after the first 5 days.
3. On diets containing from 10 per cent to 57 per cent of protein there is no definite relation between the level of protein consumption and the rate and degree of growth from 5 to 40 days after the operation.
4. When rats are given a 1 per cent protein diet for 10 days before the operation a continuation of this diet reduces the initial growth of the remaining organs and leads to a cessation of growth after the first 2 days.