The presence and levels of trans- and cw-ribosylzeatin, trans- and ds-zeatin, A^-isopentenyladenosine, and 6-(3-methyl-2-butenylamino)-9-j8-D-glucopyranosylpurine were determined in the root, and the stem and leaf of young sweet-potato plants by mass spectrometry using deuterium-labeled standards. The 6-(3-methyl-2-butenylamino)-9-j8-D-glucopyranosylpurine level was found to be the highest in both the root, and the stem and leaf. fra«s-Ribosylzeatin was present at a high level in the root. The ratio of the trans- and ds-isomers of zeatin in the root, and in the stem and leaf were determined to be 10 and 2.4, respectively. The variation in the transIds ratios of both zeatin and ribosylzeatin may reflect the growth stage of the organ in the plant.