I am indeed grateful for the honor of the Borden Award of the American Academy of Pediatrics. At this time it is fitting that I express my indebtedness to three great teachers in pediatrics whose influence has been of the utmost importance to me: Grover Powers, Daniel Darrow and Edwards Park. I should also remind you that this award is really a recognition of the joint work of my wife, Dr. Helen C. Harrison, and myself. We have both participated in all aspects of experiment and theory which will be summarized in this paper. It is a great privilege to be asked to present to the American Academy of Pediatrics observations that we have made on a problem that historically has had tremendous significance to pediatricians. A review of the history of rickets and of the discovery of vitamin D is exciting in part because of the brilliant success achieved in the solution of all important problem, but also because of the number of American leaders in pediatrics who participated in this triumph over a disease that had afflicted children in Europe and the United States for generations. THE FIRST experimental evidence of the existence of a fat-soluble organic substance with antirachitic properties was submitted by the British nutritionist Mellanby in 1918.