A panel of monoclonal antibodies, seven against the trimeric and seven against the monomeric forms to outer membrane protein D (OmpD) of Salmonella typhimurium were produced. The specificities of these monoclonal antibodies for the porin proteins of S. typhimurium and their cross-reactions with Salmonella porins OmpC and OmpF were determined by Western immunoblotting and enzyme-linked immunosorbent assay. We observed that OmpD shared more epitopes and had greater structural similarity with OmpC than with OmpF.