CD4+ and CD8+ cytotoxic T-cell (CTL) clones, selected for T-ceII-receptor (TcR)-dependent lysis of the autologous tumor and isolated from peripheral-blood lymphocytes (PBL) or tumor-infiltrating lymphocytes (TIL) of 3 melanoma patients, were characterized for the pattern of 13 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 basts of differential production of IL-1 p, IL-2, IL-6, IL-8, IL-10, TNF-α, TNF β and IFN-γ. 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-1, IL2, 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-α and-β, TNF-γ and GM-CSF after activation with only 1 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. © Wiley-Liss, Inc.