Mapping of antigenic determinants of the Leishmania infantum Hsp70 was studied by analysis of the reactivity of sera from dogs with natural visceral leishmaniasis against a collection of peptides representing overlapping sequences of the Hsp70. Despite the considerable variation in the immune response among individuals three immunodominant regions were revealed encompassing residues 241 to 260 (region I), 435 to 469 (region II) and from amino acid 601 to the carboxyl-terminal end of the protein (region III). Since anti-peptide H17 antibodies purified from a pool of leishmaniasis sera recognized the L. infantum Hsp70 and since they did not react with the homologous Hsp70s from other trypanosomatids, such as Trypanosoma cruzi, Trypanosoma rangeli and Leishmania panamensis, it was concluded that peptide H17 (region I) contains an immunodominant B cell species-specific epitope. Our data indicate, however, that the complete recombinant L. infantum Hsp70 protein cannot be used as a disease-specific tool for serodiagnosis since it is also recognized by the sera from patients with Chagas' disease.