Cytotoxic T cells (CTL) may play an important role in host defence against mycobacterial infections. CD4 CTL are preferentially induced by mycobacteria, but both CD4 and CD8 CTL may be necessary components of a protective immune response. The 65-kD mycobacterium heat shock protein (hsp65) is a poor inducer of CTL in multibacillary leprosy (MB) patients. In this study we evaluate the possible role of cytokines in modulating the cytotoxic activity of CTL from leprosy patients and normal individuals (N) against autologous macrophages presenting Mycobacterium leprae hsp65. Our results show that hsp65-specific CTL were generated from both CD4 and CD8 lymphocytes. In N, individual cytokines as well as the combination of them were able to modify the hsp65-induced cytotoxic activity. The effect of cytokines on leprosy patients' lymphocytes was different in MB and paucibacillary (PB) patients. Thus, IL-6, IL-2, IFN-γ or TNF-α did not modify the generation of hsp65-CTL from either MB (with or without an erythema nodosum episode (ENL)) or PB. In all the patients the simultaneous addition of two cytokines was required in order to increase CTL generation. In MB, IL-6 plus IFN-γ or IL-2 increased both CD4 and CD8 CTL, while TNF-α plus IFN-γ up-regulated only CD4 CTL. In PB, CD8 CTL were prominent with IL-6 plus IFN-γ, while the increase was significant in CD4 CTL with IL-6 plus IL-2. Down-regulation of CTL was observed by addition of IL-4, IL-10, anti-IFN-γ or anti-TNF-α in N controls. Our data demonstrate that IFN-γ and TNF-α must be present for at least the first 60h of the induction stage in order to generate full hsp65 CTL. Hence, IFN-γ and TNF-α would be key factors in the generation of hsp65 CTL.