The recent isolation and synthesis of vitamin B1(thiamin)1has placed in the hands of clinicians and students of nutrition alike a most valuable therapeutic agent as well as dietary essential in pure form. Clinical trial of this substance in the United States over a comparatively short period has already yielded results so striking as to warrant consideration of the question of the adequacy of American dietaries with respect to vitamin B1. It has been generally recognized that the dietaries in common use in the Orient and certain other parts of the world where beriberi is endemic are seriously deficient in this factor, but until comparatively recently it has been questioned whether this is true also for the United States and European countries. The recent and remarkable successes attending the use of pure vitamin B1, often in conditions in which lack of this factor seemed quite unlikely,