Indolamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase are two enzymes that degrade tryptophan to N-formylkynurenine. The gene (TDO2) for tryptophane 2,3-dioxygenase has been localized to 4q31-->32. We now report localization of INDO (the gene encoding indolamine 2,3-dioxygenase) by fluorescent in situ hybridization to 8p12-->p11.