RNA-protein crosslinks were introduced into Escherichia coli 30S ribosomal subunits by treatment with 1-ethyl-3(3-dimethylaminopropyl)carbodiimide (EDC). Complexes of 16S rRNA cross-linked to 30S ribosomal proteins were isolated and hybridized with a series of single-stranded bacteriophage M13-rDNA probes. These probes, each carrying an inserted rDNA fragment, were used to select contiguous 16S rRNA sections covering all of domain 1 and the major part of domain 2 (starting at the 5'-P terminus and ending at nucleotide 869) and the proteins covalently linked to each of these sections were identified by 2-dimensional polyacrylamide gel electrophoresis. This procedure identified proteins S4, S5, S7, S8, S11, S12, and S18 as the species most efficiently crosslinked to domains 1 and 2 of 16S rRNA. These results are discussed in the light of current knowledge of the tertiary structure of 16S rRNA in the E. coli 30S ribosomal subunit.