This study investigates the fate of 14C labelled 2, 4-D used as_??_trigger compound during callus induction (dedifferentiation). It also traces the special relationship of 2, 4-D with some high molecular weight components in vivo, in which 2, 4-D-2-14C was found com-bined with high molecular weight component-fractions. Nucleic acids showed very low radioactivities, based on MAK column chromatography and centrifugal profiles from sucrose density gradient treatments, but there was no specificity in this radioactive incorpo-ration. Centrifugal profiles and Pronase treatment indicate that protein combines with 2, 4-D-2-14C. These results support the claim for a model of auxin-induced derepression, in which auxin interacts with its binding protein.