Growth factor V for bacilli of the influenza group has recently been identified as a codehydrogenase (cozymase or coferment).1The Lwoffs1ahave shown that bacilli of this group which require the factor cannot synthesize it from its components, nicotinic acid amide, adenylic acid, ribose and phosphoric acid. Because of the well known importance of nicotinic acid and nicotinic acid amide in the treatment of human pellagra,2it seemed important to investigate the content of factor V in the blood of pellagrins, for the cozymase of von Euler3and the coferment of Warburg4are the only two known active biologic substances in which nicotinic acid amide is found. We have shown that B. influenzae can be used to measure accurately the cozymase content of the blood in normal persons and in pellagrins. Furthermore, prolonged treatment of several hundred pellagrins with nicotinic acid has shown that in