A soil organism, Pseudomonas indoloxidans, oxidizes indol to indigotin in solution cultures and on agar media. Indigotin is formed as crystals outside the organism, appearing first within 20 hrs. on agar media. The crystals decrease in number with increasing distance from bacterial growth. Indol does not act as a source of energy. Of a number of C compounds tested, glycerol appears most readily to serve as an energy source. Bacterial numbers and amount of indigotin produced increase with higher C:N ratios. The organism can utilize tryptophan as an energy source but produces neither indol nor indigotin therefrom. Indol is oxidized only by young growing cultures, and can be oxidized in absence of other N compounds; it is also toxic to the bacteria. No trace of indoxyl has been found in cultures, and the indigotin is not further oxidized to isatin. Two other soil organisms, Mycobacterium globerulum and Micrococcus piltonensis (Gray and Thornton), can also produce small amounts of indigotin on indol agar only.