Carboxyl-labeled IAA-,4C was predominantly transported in the acropetal direction, when applied to intact vertical or horizontal pea roots. The velocity was several cm per hour, suggesting transport in the phloem. A large proportion of the auxin entering the roots became bound. The major part of the IAA-'4C applied to the root surface was decarboxylated. Three methods of auxin application were used, viz. in 1 p.1 droplets of an aqueous solution, in lanolin paste, and by means of anion-exchange resin beads.