Much has been written about the advantages of breast feeding over artificial feeding of infants but the emphasis has been placed on the effect during the first two years of life. Few, if any, investigations have been made bearing on the later physical and mental development of the babies. It is our purpose in this article to report, with no attempt at interpretation, the results of tests and measurements made on 383 children, ranging in ages from 7 to 13 years and grouped according to the length of the period of exclusive breast feeding. The data here presented are a part of a study of growth, now in preparation for publication, which was made under the auspices of the Elizabeth McCormick Memorial Fund in Joliet (Ill.) public schools during the last five years. Development and growth were determined by medical examinations of the children stripped, made by Drs. Stanley Gibson,