A chemically defined medium, composed of inorganic salts, glucose, asparagine, cystine, and a vitamin supplement, has been devised for growth of the yeast phase ofHistoplasma capsulatum. Growth in this medium was abundant and compared favorably with that in media containing complex natural material. Conversion of each of the 20 strains examined was accomplished by one or more passages on agar slants of the medium and incubation of the cultures at 37° C. Yeast phase cultures on this medium have been stored for 6 months or more at approximately 4° C without conversion or loss of viability. Of the 20 strains examined for vitamin requirements of the yeast phase, all were partially deficient for thiamine; nine for inositol; five, either partially or completely deficient for niacin; and one, completely deficient for biotin. No specific amino acid was required for growth of the yeast phase, but an organic source of sulfur and one of nitrogen were essential. Cystine and cysteine were equally effective for growth of the yeast phase when supplied on an equivalent sulfur basis and very little difference in growth occurred in media which contained equal amounts of nitrogen in any one of the following compounds: asparagine, glutamic acid, aspartic acid, and proline, Of the 20 strains, all but one, which requires biotin, were capable of continued growth in the mycelial phase when subcultured on an agar medium containing only inorganic salts and dextrose, but growth was improved significantly by asparagine or casein hydrolysate.