When zeatin was supplied to excised leaves of Populus alba, the principal metabolites formed were adenosine, O-β-D-glucopyranosyl-cis-zeatin (derived from cis-zeatin in the commercial zeatin used), O-β-D-glucopyranosylzeatin, and two new metabolites, namely, O-β-D-glucopyranosyldihydrozeatin and O-β-D-glycopyranosyl-9-β-D-ribofuranosyldihydrozeatin, the structures of which were confirmed by unambiguous synthesis. Chromatographic studies indicated that adenosine 5'-phosphate, zeatin 7-glucopyranoside, zeatin 9-glucopyranoside, dihydrozeatin and zeatin 9-riboside were minor metabolites. The principal metabolites of zeatin 9-riboside in P. nigra leaves were the new metabolites O-β-D-glucopyranosyl-9-β-D-ribofuranosylzeatin (synthesized chemically) and O-β-Dglucopyranosyl-9-β-D-ribofuranosyldihydrozeatin.