The metabolism of (E)-[ 3 H]2-ethylhex-2-enoic acid (EHA) was studied in excised seedlings of barley (Hordeum vulgare). It was rapidly taken up from the nutrient medium. The metabolites, isolated by extraction with methanol, separated and purified by TLC and HPLC, were identified by enzymatic, chemical, and spectrometric methods, especially 1 H-NMR spectroscopy. The time course of metabolism during 6 , 12, 24, 48, and 72 h is presented, indicating interconversation reactions. A rapid conjugation with glucose was observed, decreasing in concentration again after longer time periods in favour of disaccharide esters, higher conjugates, and a hydroxylation product which was present in free and conjugated form.