The invention relates to the field of combating leishmaniases. Said invention results from the isolation, from wild isolates of Leishmania major, of a protein-coding gene known as LmPDI which has two regions that are identical to the sequence (Cys-Gly-His-Cys) of the potential active site of the protein disulphide isomerase (PDI). The LmPDI protein is predominantly expressed in the most virulent isolates of the parasite. Said protein forms a novel therapeutic target for developing anti-leishmaniasis medicaments and a novel element that can be used in the composition of immunogenic, and possibly vaccinating, preparations which are intended to protect a human or animal host against Leishmania.