A monoclonal antibody (MAb) was developed by Jaradat and Zawistowski (1998) against an outer membrane 35K protein using whole, heat attenuated cells of 'Salmonella typhimurium'. This MAb was designated as MAb 1D6 and identified as being of the immunoglobulin A (IgA) class. Outer membrane 35K protein, if antigenetically stable, could be a very useful serological and epidemiological marker of Salmonellae spp. To assess the stability of the 35K protein, outer membrane protein (OMP) extracts were prepared from several species of 'Salmonella' grown under various environmental conditions. These conditions included factors such as pH, osmolarity and heat treatment. The antigenicity of the outer membrane 35K protein was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) followed by immunoblotting. Electrophoretic results showed that bacteria grown under stres ful conditions produced several additional minor outer membrane proteins. This could have been due to the structural alteration of the 35K protein, since existing minor polypeptides had common antigenic properties. Furthermore, it was observed that production and antigenicity of the 35K protein was always conserved despite environmental treatment of the bacteria.