Eighty-two strains of Bacillus polymyxa grew in a medium consisting of inorganic salts, glucose, and casein hydrolysate only when biotin was added, hence this growth factor may be considered essential. Thiamin stimulated growth of some strains but inhibited others whereas pantothenic acid, nicotinic acid, riboflavin, pyridoxine, and inositol were without effect. Casein hydrolysate was replaceable by urea, ammonium sulphate, and a mixture of 18 amino hydrolysed acids, but with a few exceptions these substances were not as effective as the protein. Potassium nitrate and asparagine were poor sources of nitrogen. Yeast extract, in a medium containing only glucose and inorganic salts, was superior to all other substances tested in its stimulatory effect on B. polymyxa.