Human infection by L. braziliensis (Lb) causes a cutaneous ulcer. Tiisue obtained from the edge of these ulcers reveal the presence of a chronic inflammatory infiltrate, sometimes with granuloma formation. This infiltrate is predominantly composed of macrophages, T and B lymphocytes and plasma cells. The presence of amastigotes in the tissue associated with Lb PCR positivity is essential for the diagnosis. Lb ulcer is most often associated with positivity for the delayed hypersensitivity skin test to Lb Ag (SLT). Our research group highlighted that SLT negative patients have more antimony therapy failure. The histopathological analysis and cellular infiltrates seen in biopsies of SLT - patients revealed less inflammation, necrosis, and a higher but not siginificant number of amastigotes. Other cells and molecules expressions such as CD20, plasm cells, IL1b, granzyme, perforin, and macropahges subtypes are under analysis in an attempt to understand whether therapeutic failure depends on more specific cellular inflammatory mechanisms.