Pleomorphism in cultures of Azotobacter vinelandii was induced by addition of Difco peptone to the growth medium. Under the conditions of the study, 5% peptone gave rise to transient forms described as "fungoid cells" which were osmotically fragile. After some 48 hr of culture, they became osmotically stable and resumed a more typical morphology. It was shown that the pleomorphism-inducing principle in peptone was glycine.