The stepwise metabolism of gibberellin A12-aldehyde (GA12-aldehyde) to GA20 is demonstrated from seedling shoots of maize (Zea mays L.). The labeled substrates [13C,3H]GA12-aldehyde, [13C,3H]GA12, [14C4]GA53, [14C4/2H2]GA44, and [14C4/2H2]GA19 were fed individually to dwarf-5 vegetative shoots. Both [13C,3H]GA12-aldehyde and [13C,3H]GA12 were also added individually to normal shoots. The labeled metabolites were identified by full-scan gas chromatography-mass spectrometry and Kovats retention indices. GA12-aldehyde was metabolized to GA53-aldehyde, GA12, GA53, GA44, and GA19; GA12 was metabolized to 2[beta]-hydroxy-GA12, GA53, 2[beta]-hydroxyGA53, GA44, 2[beta]-hydroxyGA44, and GA19; GA53 was metabolized to GA44, GA19, GA20, and GA1; GA44 was metabolized to GA19; and GA19 was metabolized to GA20. These results, together with previously published data from this laboratory, document the most completely defined gibberellin pathway for the vegetative tissues of higher plants.