The rate of individual ribosomal protein synthesis relative to total protein synthesis has been determined in Escherichia coli rel+ and rel- cells, under valyltRNA deprivation. These strains have a temperature-sensitive valyl-tRNA synthetase. Starvation was obtained following transfer to the cells to non-permissive temperature. Ribosomal proteins were obtained by treatment of either total lysates of freeze-thawed lysozyme spheroplasts or ammonium sulphate precipitate of ribosomes, with acetic acid. Differential labelling of the ribosomal proteins was observed in both strains: proteins from the rel+ strain appear more labelled than those from the rel- strain, the rate of labelling of individual proteins being about the same in both strains. Moreover ribosomal proteins were found as stable during starvation as total protein. It is thus concluded that in starving cells individual ribosomal proteins are not synthesized at equal rates. This indicates that the synthesis of ribosomal proteins is not only under the control of the rel gene.