Eight strains were used in this study. Opt. growth was obtained at a level of 17.5 mg. N/10 ml. medium. An acid hydrolysate of casein can be replaced by 9 amino acids, - L-arginine, DL-phenylalanine, L-tyrosine, DL-leucine, DL-isoleucine, DL-valine, L-tryptophane, DL-throenine, and DL-methionine. For max. growth of most strains 3 vits.[long dash]p-aminobenzoic acid, thiamine and biotin[long dash]are essential. One strain requires, in addition, nicotimc acid and pyridoxine. Two strains, which require no thiamine for growth, also produce no toxin. Citrovorum factor or folic acid replaces para-aminobenzoic acid, and biotin is replaced by oleic acid or Tween. Toxin production in the defined medium is low, indicating that the essential factors for growth and toxin production are not identical.