One of the functions expressed by the effectors of the immune system is the synthesis of cytokines, either in soluble form or associated with the membrane. Study of this communication network between the different compartments of the immune system can be conducted either in the blood (serum) of leprosy patients or directly in the infected tissues. The key to how the immune response will develop lies in the nature of the cytokines produced locally by the immune cells. For the characterization and detection of cytokines/lymphokines we may use either biological methods (bioassay), or antibody-based detection systems (RIA, Elisa, Elispot, immunocytochemistry using monoclonal antibodies), or techniques derived from molecular biology (Polymerase chain reaction-PCR, analysis of messenger RNA, and hybridization in situ). These various techniques, whose advantages and disadvantages are discussed, have demonstrated that locally, in the infected lesions, resistance and/or susceptibility to M. leprae infection correlates with differing cytokine secretion profiles.