To improve the immune potential of porin (a pore-forming protein of Salmonella sp.), different immunopotentiators such as Freund's complete adjuvant (FCA), lipopolysaccharide (LPS) and polyoxydonium (PO) were evaluated by studying the nature of the protective immune response induced against murine Salmonellosis. The nontoxic, synthetic heteropolymer polyoxydonium was as good as LPS at inducing antiporin immunoglobulin G (IgG) antibodies and protective immunity. Analysis of the antiporin IgG subclass pattern revealed a preferential increase in a particular subclass based on the immunopotentiator used. Porin, alone or emulsified in FCA, elicited predominantly antiporin IgG 1 antibodies, whereas LPS preferentially evoked antiporin IgG 2a , IgG 2b and IgG 3 antibodies. Polyoxydonium induced a clear shift towards antiporin IgG 2b antibodies. The significance of these antiporin IgG subclass antibodies in protection against murine Salmonellosis was studied by passive immunization and by analysing the infected mouse sera.