The clinical diagnosis of cutaneous leishmaniasis in the majority of cases presents no difficulty. This is not true, however, of the lesions of mucous membranes, particularly in those cases in which there are no associated lesions of the skin. In such cases the differential diagnosis from syphilis, tuberculosis and blastomycosis may not be easy. Search for parasites in smears and sections is frequently negative, particularly if specific therapy, such as intravenous injections of tartar emetic, has already been instituted. The histologic features of the lesion, though easily distinguished from tuberculosis and blastomycosis, may be confused with syphilis. The therapeutic test, that is, the administration of tartar emetic, may give no aid, since, as is well known, the mucous lesions are notably refractory to treatment. Antisyphilitic treatment might be more helpful, though there would remain the possibility of a third undetermined infection in those cases in which the Wassermann reaction was