Three ribonucleosides responsible for cytokinin activity in Euglena gracilis var Bacillaris tRNA have been isolated and identified as 6-(3-methyl-2-butenylamino)-9-beta-D-ribofuranosylpurine, 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-beta-D-ribofuranosylpurine, and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-beta-D-ribofuranosylpurine. The structures of these compounds were assigned on the basis of their chromatographic properties and ultraviolet and mass spectra which were identical with those of the corresponding synthetic compounds. The elution profiles of cytokinin bioassay activity and of 35S radioactivity suggest the presence of a trace amount of 6-(3-methyl-2-butenylamino)-2-methylthio-9-beta-D-ribofuranosylpurine.