From a collection of monoclonal antibodies (MAbs) that recognize the native structure of the toxin-coregulated pilus of Vibrio cholerae, two protective MAbs (16.1 and 169.1) were used to localize the corresponding epitopes on the pilus. These MAbs were shown to specifically recognize the carboxyl half of the TcpA pilin subunit, as determined by their recognition of proteolytic fragments and hybrid pilin proteins. The positions of the epitopes were precisely determined through the use of overlapping synthetic peptides corresponding to this region of the pilin. The MAbs were found to recognize adjacent peptides, delineating a region between residues 157 and 199. Since the protective nature is specific for these two antibodies, the findings suggest that this region defines a domain that participates in toxin-coregulated pilus-mediated colonization and therefore represents a target for studies of its potential as an immunogen for incorporation into a component cholera vaccine.