The paucity of data concerning the magnesium needs of man at different periods of his development has stimulated further study of magnesium retentions in children. The first report1 from this laboratory, which included a review of the literature, was concerned primarily with a series of single ten day balance studies with individual children. Calcium and phosphorus retentions also were studied in order to determine if there are any interdependent relations among these three metabolites.
The present report represents part of a nine month study of the growth, osseous development and mineral metabolism of 3 preschool boys aged 4 years 10½ months, 4 years 9 months and 3 years 3 months, respectively, at the beginning of the study and considers the magnesium retentions at three levels of ingestion, any one of which might occur in a seemingly well selected diet. Data pertaining to the calcium, phosphorus and nitrogen retentions and