Mammalian ribosomal protein (rp) genes are members of multigene families which are composed predominantly of multiple processed pseudogenes and one functional intron-containing gene. The presence of multiple pseudogenes has hampered the isolation and study of the functional rp genes. We have recently developed a polymerase chain reaction (PCR)-based strategy for the detection of intron-containing genes in the presence of multiple pseudogenes (B. Davies, S. Feo, E. Heard, and M. Fried, 1989, Proc. Natl. Acad. Sci. USA 86: 6691-6695). We have used this technique to identify the intron-containing PCR products of seven human rp genes (rpL19, rpL30, rpL35a, rpL36a, rpS6, rpS11, rpS17) and to map their chromosomal locations. No linkage was found between any of these seven rp genes nor was linkage found to the three other rp genes previously mapped. The wide distribution of the rp genes throughout the human genome strongly suggests that the coordinate regulation of the expression of mammalian ribosomal proteins in response to the cell's varying requirements for protein synthesis is not a result of cis activation of chromosomal regions but is mediated by trans-acting factors.