Abstract: A metabolic product, present in the culture media of Ustilago esculenta P. Henn., has been identified as indole acetic acid (IAA). The identification of this compound was based upon the split-soybean curvature test, four independent color tests, paper chromatography and the absorption spectrum in ultra-violet light, as compared with those of the known synthetic compound. Peptone, gelatin, casein hydrolysate, fat-free milk and a number of amino acids were used as the nitrogen source in the culture media. Tryptophan appeared to be the only primary precursor of IAA in Ustilago esculenta. One of the intermediary products identified by paper chromatography seemed to be indole acetaldehyde. The indole acetaldehyde is thought to be produced from tryptophan through indole pyruvic acid. Evidence is presented to show that tryptamine is not an intermediate metabolite for IAA production in this microorganism.