Detailed studies of ribosomal proteins, essential components of the protein biosynthetic machinery, have been hampered by the lack of readily accessible chromosomal deletions of the corresponding genes. Here, we report the systematic genomic deletion of 41 individual ribosomal protein genes in Escherichia coli, which are not included in the Keio collection. Chromosomal copies of these genes were replaced by an antibiotic resistance gene in the presence of an inducible, easy-to-exchange plasmid-born allele. Using this knockout collection, 9 ribosomal proteins (L15, L21, L24, L27, L29, L30, L34, S9 and S17) were found nonessential for survival under induction conditions at various temperatures. Taken together with previous results, this analysis revealed that 22 of the 54 E. coli ribosomal protein genes can be individually deleted from the genome. These strains also allow expression of truncated protein variants to probe the importance of RNA-protein interactions in functional sites of the ribosome. This set of strains should enhance in vivo studies of ribosome assembly/function, and may ultimately allow systematic substitution of ribosomal proteins with RNA.