The distribution of the two cytokinin-active ribonucleosides 6-(3-methyl-2-butenylamino)-9-β-D-ribofuranosylpurine (1) and 6-(3-methyl-2-butenylamino)-2-methylthio-9-β-D-ribofuranosylpurine (2) in tRNAPhe, tRNAUUGLeu, tRNAUCRSer, tRNATyr, tRNACys, and tRNA2Trp from stationary phase Escherichia coli has been studied. Compound 2 predominated in all these species except tRNAPhe, in which compound 1 was greatly in excess. Compound 1 was present in relatively small amounts in tRNAUUGLeu, tRNACys, and tRNA2Trp, and was not detected in tRNAUCRSer and tRNATyr. Cells from the early logarithmic phase had the highest cytokinin content in their tRNA. Stationary phase tRNA had a slight increase in the amount of 1, which may be explained by the appearance of the new tRNAPhe. No differences were observed between the chromatographic patterns of tRNAs from early-, mid-, and latelogarithmic phases.