Summary Feeding of [8- 14 C]adenine to immature caryopses of Zea mays for periods of up to five days did not result in the incorporation of any radioactivity into compounds with similar chromatographic properties to those of the authentic cytokinins. The lack of a positive correlation was apparently not due to synthesized compounds being metabolized at a rapid rate as the caryopses did contain considerable cytokinin-like activity. The application of [8- 14 C] t -zeatin also indicated that six hours after application the major portion of the applied cytokinin was still unmetabolized. The applied adenine was rapidly converted to adenosine and this subsequently to unidentified polar derivatives. Zeatin apparently followed a number of different metabolic routes. These included side chain cleavage as evidenced by the detection of a radioactive molecule tentatively identified as adenine; saturation of the side chain as indicated by a compound which co-chromatographed with dihydrozeatin; and ribosylation of the purine ring as supported by the detection of radioactive compounds co-chromatographing with adenosine, ribo-sylzeatin and dihydroribosylzeatin. No evidence for glycosylation or phosphorylation of the applied zeatin was detected.