The enzymic or nonenzymic oxidation of indole-3-acetic acid (IAA) was promoted in the presence of the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The involvement of DPPH with the IAA free-radicals in the nonenzymic and the peroxidase-catalyzed oxidations was discussed. Methylene-oxindole was identified as a breakdown product of IAA, indicating a pathway operative with this radical.