Forty eight clinically arrested lepromatous patients were submitted to several tests to evaluate cellular immunological competence (PPD, Trichophytin, DNCB, determination of the percentage of T lymphocytes in the peripheral blood, and early and late reactions to the lepromin). The results of the Trychophytin test and of the lymphocyte percentage test did not differ from those of the control group, whereas the results to the PPD test were more often positive for the arrested Virchovian cases. All the patients presented positivity to the DNCB test, and none of them showed positivity to the Fernandez reaction. As for the late reaction to the lepromin, all the patients were negative, although in histopathological testing four degrees of reactivity was observed ranging from focal, non specific inflammatory reaction to granulomatous histiocytic with an epithelioid outline. By means of these results the authors were able to confirm that: 1. There is no cross reactivity between the PPD and lepromin tests. 2. Sulfone therapy does not interfere in immunocellular results for the tests employed. 3. Lepromatous patients respond like the general population to the unspecific sensitivity tests utilized. 4. The finding of histiocytic reaction with epithelioid outline in some biopsies of Mitsuda reaction in lepromatous patients, suggests the presence of a sub-population within this group, probably Borderline patients that suffered during the infection's evolution downgrading of theirs clinic and histological characteristics.