Combined gas chromatography-mass spectrometry (GCMS) was used to identify and quantify specific cytokinins from Porphyra perforata J. Ag. and Sargassum muticum (Yendo) Fensh. The level of isopentenyladenosine was estimated to be 0.6-mu-g.kg-1 fresh weight in Porphyra and 0.9-mu-g.kg-1 fresh weight in Sargassum. The level of cis-zeatin riboside was estimated to be 0.2-mu-g.kg-1 fresh weight in Sargassum. This is the first definitive identification of a cytokinin from a red alga, and the second report from a brown alga.