In the present study we show that sera from dogs naturally infected with the protozoan parasite Leishmania infantum contain antibodies that specifically react with the parasite histone H3. Using synthetic peptides covering the complete sequence of the protein we located the linear antigenic determinants within the 40 amino-terminal amino acids of the molecule. In addition to the complete form of the protein (rLiH3), two regions of the Leishmania histone H3 were expressed as recombinant proteins: the rLiH3-Nt fragment containing the 39 amino-terminal amino acids and the rLiH3-Ct fragment containing the 90 carboxyl-terminal residues. Competition experiments using the protein fragment rLiH3-Nt as competitor confirmed that the antigenic determinants of histone H3 are confined to the amino-terminal domain. This domain, which is believed to be exposed on the nucleosome surface, is also the most evolutionarily divergent region of the L. infantum histone H3. Visceral leishmaniasis (VL) sera do not react with mammalian histones, an indication that the anti-histone response elicited during Leishmania infection is triggered by the parasite histone. The results of the prevalence of anti-histone H3 antibodies in canine VL sera together with the sequence-specific characteristics of the amino-terminal region of L. infantum histone H3 indicate that the recombinant protein rLiH3-Nt may be of use for diagnosis of canine VL.