In spite of the voluminous literature that has been published on the metabolism of calcium and phosphorus, little has been written in regard to the minimum requirements of these minerals for growing children. The only two papers which we were able to find dealing directly with the subject were those by Sherman and Hawley1 and Willard and Blunt.2 However, neither of them lowered the calcium and phosphorus intake sufficiently to obtain a negative balance. Hence the minimum requirement was not established. In our study of the metabolism of undernourished children, we have obtained a great range of values in calcium and phosphorus balance. Owing to the difficulty in making some of the children eat the calculated amount of food, the calcium and phosphorus intake often fell below the minimum requirement. The following paper was therefore compiled from results obtained in this study, supplemented with additional experiments in order