Transfer RNAs were separated into a ribosome bound fraction and a supernatant (cytoplasmic) fraction. The nucleoside composition, 2-dimensional PAGE pattern and in vivo labeling were compared. 12 minor nucleosides were identified by HPLC. In general, the minor nucleosides, especially N2-methyl-guanidine and ribothymidine, were higher in the ribosome-bound fraction. The PAGE patterns were similar but there were quantitative and qualitative differences among the smaller spots. In vivo labeling by 32P showed that new tRNA goes preferentially to the ribosome but mixing does occur. The results suggest the existence of two compartments of tRNA.