CD4+ and CD8+ cytotoxic T-cell (CTL) clones, selected for T-cell-receptor (TcR)-dependent lysis of the autologous tumor and isolated from peripheral-blood lymphocytes (PBL) or tumorinfiltrating lymphocytes (TIL) of 3 melanoma patients, were characterized for the pattern of I3 different cytokines released by antibody-or tumor-mediated triggering. Induction or enhancement of cytokine release by anti-CD3 monoclonal antibody (MAb) led to the identification of 2 major sub-sets of CD8+ CTL clones on the basis of production of IL-4. Within the 2 groups of IL-4-producing or non-producing clones, further sub-sets could be identified on the basis of differential production of IL-la, IL-2, IL-6, IL-8. IL-10, TNF-a, TNF and IFN-y. A similar analysis performed on a panel of CD4+ CTL clones indicated multiple patterns consistent with at least 4 major sub-sets, but further complexity was evident in each sub-set on the basis of differential production of IL-I, ILZ, IL-6, IL-10 and G-CSF. The cytokine profile of CD4+ and CD8+ clones, as determined after anti-CD3 stimulation, was different from the pattern seen after co-culture with autologous tumor, since many clones released cytokines such as IL-4, IL-10, IFN-aand -y, TNF-a and GM-CSF after activation with only I of the 2 stimuli. These results indicate that CD4+ and CD8+ CTL clones reacting to human melanoma belong to a highly complex repertoire of functional subsets characterized by distinct cytokine profiles. In addition, the cytokine pattern of each T-cell sub-set can be modulated by changing the activation signals delivered to the T cell.