The intradermal inoculation in naive or in previously sensitized individuals of small amounts of Leishmania extract (Montenegro's skin test) induced or modulated, respectively, the immune response to Leishmania, as assessed by subsequent Montenegro's skin tests. These phenomena could hinder the interpretation of Montenegro's skin tests in a population already subjected to the test in the past and, in addition, could affect in an unknown way the development of mucosal lesions in people infected with L. braziliensis or L. amazonensis, since those lesions have been associated with hypersensitivity to Leishmania antigens. Anti-Leishmania antibody responses, assessed by enzyme-linked immunosorbent assay, were not induced in naive individuals by Montenegro's skin tests, but tended to become more intense following these tests in previously sensitized individuals