The immunogenicity of a multiple antigenic peptide construct consisting of four copies of the synthetic 21-mer peptide DANFDSIRVDAVDNVDADLLQ was measured. The composition of this peptide was derived from a sequence in the N-terminal region of mutans streptococcal glucosyltransferases (GTFs) containing an aspartic acid implicated in catalysis. The peptide (CAT) construct was synthesized as a tetramer on a lysine backbone and subcutaneously injected into Sprague-Dawley rats for polyclonal antibody formation or intraperitoneally injected into BALB/c mice, and then spleen cell fused with Sp2/0Ag14 murine myeloma cells for monoclonal antibody formation. The resulting rat antisera and mouse monoclonal antibodies reacted with CAT and with native GTF isozymes from Streptococcus sobrinus and Streptococcus mutans (in enzyme-linked immunosorbent assay and Western blot [immunoblot] analyses). Functional inhibition of the water-insoluble glucan synthetic activity of S. sobrinus GTF-I was demonstrated with an immunoglobulin M anti-CAT monoclonal antibody (> 80% inhibited) and with rat sera (approximately 17% inhibited). The monoclonal antibody preparation also modestly inhibited the water-soluble glucan synthetic activity of an S. mutans GTF mixture. These results suggest that the CAT peptide contains B-cell epitopes that are similar to those of intact mutans streptococcal GTFs and has the potential to elicit antibody that can inhibit GTF function. Thus, sequences within this peptide construct may have value for inclusion in a synthetic dental caries vaccine.