Shiga toxin B chain, the binding subunit of Shiga toxin, was recently purified; and the amino acid sequence of this 7,716-dalton polypeptide was determined (N.G. Seidah, A. Donohue-Rolfe, C. Lazure, F. Auclair, G. T. Keusch, and M. Chretien, J. Biol. Chem. 261:13928-13931, 1986). In the present study, synthetic peptides corresponding to three overlapping sequences from the N-terminal region of this subunit were prepared. The peptides synthesized consisted of residues 5 to 18, 13 to 26, and 7 to 26. This region coincides with the major peak of hydrophilicity and surface area residues predicted from a computer analysis. For the purpose of immunization, the peptides either were conjugated with a protein or synthetic carrier or were polymerized with glutaraldehyde. Antisera against these peptide derivatives raised in rabbits reacted not only with the respective homologous peptide but also to a comparable extent with the intact Shiga toxin. The anti-peptide antisera effectively neutralized the various biological activities of the Shiga toxin, namely, cytotoxicity to HeLa cells, enterotoxic activity (the fluid secretion into ligated ileal loops in rats), and neurotoxicity in mice. Furthermore, active immunization with the peptide conjugates was found to protect mice against the lethal effect of Shiga toxin.