Culture conditions for the exclusive development of the mycelial and the yeast forms of Sporothrix schenckii from conidia in a rich, defined medium were established. Only the mycelial morphology developed when the pH of the medium was adjusted between 4.0 and 5.0 and the conidia were incubated at 25 degrees C, regardless of aeration. When the pH of the medium was adjusted between 6.5 and 8.0 and the conidia were incubated with aeration at 35 degrees C, only the yeast form was obtained. Using these culture conditions conidia were inoculated in a buffered-salts medium with vitamins with or without added carbohydrates as carbon sources. After incubation, the form obtained was recorded and the amount of growth determined on a dry weight basis. Development of the mycelial form was observed with all of the carbon sources tested (glucose, fructose, mannose, arabinose, maltose, sucrose and starch) while the yeast form developed only when glucose or another hexose was added to the medium. These observations indicated that in S. schenckii the development of conidia into a specific form is dependent on the interrelationship between the available nutrients and the culture conditions and that no specific parameter seemed to be exclusively determinant of the morphology obtained.