It would be medically and economically desirable to prevent the millions of annual extraintestinal infections and the thousands of associated deaths due to Escherichia coli. Outer membrane proteins are potential vaccine candidates for the prevention of these infections. This study tested the hypotheses that the siderophore receptor IroN is antigenic and that an IroN-specific antibody response confers protection in vivo. Subcutaneous immunization with denatured IroN resulted in a significant IroN immunoglobulin G (IgG)-specific response in serum (P < 0.0001) but not a systemic or mucosal IroN-specific IgA response. In a mouse model of ascending urinary tract infection, subcutaneous immunization with denatured IroN conferred significant protection against renal (P = 0.0135 and 0.0095 in two independent experiments), but not bladder, infection. These data, together with the previously demonstrated role of IroN in virulence, its expression in human biologic fluids, and its prevalence among extraintestinal pathogenic E. coli strains, support further studies on the role of IroN as a vaccine candidate.