The purpose of this study was to compile a table of the reported magnesium contents of 100 gram portions of commonly used foods and to calculate the magnesium content in the certain experimental diets given to 12 preadolescent girls during 53 days in the summer of 1958, The subjects were six and one-half to nine years of age. Each subject was of normal math and weight for their height and age. The diets were adequate in all nutrients as recommended by the National Research Council (34) except for the nitrogen intake which averaged 3.46 grams daily for five six-day periods, and 2.83 grams for the following three six-day periods.