Because of the recent evidence of involvement of cytokines in the inflammatory processes, cellular proliferation and host defence mechanism, we have measured the in vitro production of interferon-gamma (IFN-gamma), interleukin (IL)-4, IL-6 and tumor necrosis factor-alpha (TNFalpha) from the phenotypically and histologically characterized ten peripheral T cell lymphoma (PTCL) cases. The immunophenotypic study had identified three gammadelta PTCL cases (CD3-CD4+ CD8+, one case and CD3+ CD4-CD8, two cases). Mononuclear cells obtained from the lymph node cells of PTCL cases, irrespective of histologic type, were found to produce highly elevated levels of IFN-gamma and IL-6 both spontaneously and in response to concanavalin A stimulations. However, IL-4 and TNFalpha production was characteristically decreased from cells obtained from both blood and lymph nodes. IL-4 and TNFalpha have a number of pleiotropic activities in particular stimulation of various immune effector functions. Their deficient production is an important indication of severe immune dysfunction in this disease. However, the meaning of their deficient production is currently unclear. It may be a loss of physiologic regulation within the cytokine network. On the contrary, elevated IFN-gamma and IL-6 production may be important in etiology, inflammatory response or disease pathogenesis.