Ten antisera raised in rabbits, against polymeric flagellins from ten different Salmonella serotypes were used to determine the relative cross-activities between salmonella flagellins in monomeric form. The results showed a high degree of cross-reactivity between the antisera (IgG antibodies) and all monomeric flagellins investigated. Consequently, it was possible to detect the ten Salmonella serotypes, after heat depolymerization of flagella using radioimmunometric assay with only one antiserum raised against polymeric flagellin from one serotype. The results also showed that native flagella differed antigenically from repolymerized and monomeric flagellins. This is possibly due to changes in the tertiary structure of sub-units of flagella when depolymerized with acid or heat resulting in unfolding and unmasking of common antigenic determinants. The unfolded and unmasked antigenic determinants were not only common to the Salmonella serotypes investigated, but also to other members of Enterobacteriaceae.