We have isolated recombinant lambda phage carrying the genes for 14 of the ribosomal proteins of the yeast Saccharomyces cerevisiae. Analysis of these and of the plasmid carrying the gene tcm1, which codes for the ribosomal protein responsible for resistance to trichodermin, demonstrates that in general the genes for ribosomal proteins are unlinked. One exceptional recombinant carries the genes for two ribosomal proteins within a 2-kilobase region. DNA fragments bearing individual ribosomal protein genes were used to probe restriction digests of the yeast genome to determine whether any of the genes were duplicated. Only 3 of 12 of the genes are present unequivocally as a single copy. Similar fragments were used to probe blots of mRNA separated on denaturing agarose gels to determine the size of the mRNA for each protein. In each case, the mRNA is near the minimum size necessary to code for its protein. In certain temperature-sensitive mutants which fail to synthesize functional mRNA for ribosomal protein, Rosbash et al. (Rosbash, M., Harris, P. K. W., Woolford, J., and Teem, J. L. (1981) Cell, 24, 679-686) have demonstrated the accumulation of a larger RNA molecule, homologous to a ribosomal protein gene, that appears to be a transcript which retains an intervening sequence. We find that for 8 of the 11 ribosomal protein genes examined, a larger molecule accumulates in such a mutant strain, suggesting that in general transcripts of ribosomal protein genes may have introns.