The nature of metabolic products of 3–indolylacetic acid (IAA) extracted from potato tuber disks treated with aerated IAA solution has been investigated. Two major products, known at first as ‘V’ and ‘P’ in these studies have been isolated and ‘V’ has been identified as 3-indolylacetylaspartic acid (IacAsp). The rapid uptake of IAA is inhibitited by metabolic poisons such as 10 −3 M. cyanide. The maximum mean internal concentration exceeds the external concentration well–aerated cultures. The mean internal concentration, however only remains for a period and then falls off rapidly as a result of extrusion of absorbed IAA into the external solution. This extrusion is not inhibited by 10 -3 cyanide; when the mean internal IAA concentration is 150 μ mol/ml. and the localized IAA concentration must therefore exceed this value. We conclude therefore that the IAA concentration in the sites where it has accumulated exceeds the concentration of IAA outside. Uptake of IAA and also its further conversion are inhibited by indolylacetonitrile and promoted by aspartate, but this promotion is not associated with any gain in amount of indolylacetylaspartate (IacAsp). The data suggest that IacAsp may be formed in tissue from ‘bound IAA’ rather then free IAA. The ‘accelerator α’ found in potato and beans which has similar R F to IAcAsp has been shown definity to be some other substance or substances and not IAcAsp as was at first thought possible.