Amastin surface proteins belong to a large family of developmentally regulated proteins comprising up to 45 members that have recently been discovered in the genus Leishmania and are highly similar to the amastin proteins in Trypanosoma cruzi. All members of the amastin gene family contain a highly conserved 11-amino-acid (aa) signature at the N terminus, which is unique to the amastin proteins and to the Trypanosomatidae family. Recent studies have demonstrated that this region is highly protective in a mouse model. The goal of the present study was to evaluate the potential of the 50-aa N-terminal domain of amastin proteins harboring the conserved 11-aa amastin signature peptide as a relevant immune biomarker of cutaneous leishmaniasis (CL) and visceral leishmaniasis (VL). We report here the amastin-binding total immunoglobulins (IgG) and/or IgG subclasses in the sera of patients at different stages of CL (n=90) and VL (n=41). In CL cases, there is no significant difference in seroreactivities between active, recovered, and nonhealed cases. However, the amastin peptide-reactive antibodies were present at high titers in 19 of 20 sera collected from patients with active VL compared to sera from patients recovered from VL and asymptomatic cases of VL. These data suggest that the amastin signature peptide could represent a relevant biomarker for the serodiagnosis of VL and, most importantly, that it could permit differentiation among the different stages of the disease.