The OmpD porin was isolated and purified from Salmonella typhimurium strain SH 7454 (ompC::Tn10), digested with cyanogen bromide (CNBr) and the peptide fragments were separated by SDS-PAGE. N-terminal sequencing identified a total of 96 residues from four distinct peptides. The sequence showed that OmpD is homologous to NmpC (75% identity), Lc (75%) and OmpC (70%) from Escherichia coli, and OmpC (68%) from S. typhimurium. The sequence was essentially identical to the translated sequence of an nmpC-like gene of S. typhimurium, currently placed at 38.6 centisomes of the chromosome. Our results and other data suggest, however, that this gene is actually the ompD gene, which is more correctly placed in the 34 centisome region of the chromosome. The CNBr-generated peptides were also screened with 16 anti-S. typhimurium OmpD monoclonal antibodies by Western blotting. These results, in conjunction with the prediction of the OmpD folding pattern based on the known three-dimensional structure of E. coli OmpF, showed a close immunological relationship among S. typhimurium OmpD and E. coli NmpC and Lc, and a strong conservation of sequences within the transmembrane ß strands of these porins and E. coli OmpC, PhoE and OmpF, and Salmonella typhi OmpC.