T lymphocytes are important both for the host defence against infections and probably also as antileukaemic effector cells in patients with acute leukaemia. To investigate the T lymphocyte cytokine repertoire of clonogenic T lymphocytes, CD4+ and CD8+ T lymphocyte clones were prepared from acute leukaemia patients with chemotherapy-induced cytopenia (leucocytes <0.5x 10(9)/l). A majority of both CD4+ and CD8+ clones secreted detectable interleukin-2 (IL-2), IL-10, IL-13, granulocyte/macrophage-colony-stimulating factor and interferon gamma (IFNgamma) in response to phytohaemagglutinin + accessory cells (Epstein-Barr-virus-transformed B cell line, 80-Gy-irradiated). The CD4+ clones showed significantly higher levels of IL-10 secretion than the CD8+ clones. Decreased levels of IL-2, IL-13 and IFNgamma were observed when acute myelogenous leukaemia (AML) blasts were used instead of cells from the B cell line as accessory cells during phytohaemagglutinin activation, but the differences in IL-13 and IFNgamma levels were reversed by addition of exogenous IL-2. On the basis of these results we conclude: (i) the remaining clonogenic T lymphocytes derived from acute leukaemia patients with therapy-induced leucopenia can respond to activation with a broad cytokine response, and T-cell-derived cytokines may then contribute to cytokine responses during complicating infections in these patients; (ii) although T cells can modulate AML blast functions and mediate antileukaemic effects, the leukaemia blasts will also modulate T cell functions and alter the cytokine profile of activated T lymphocytes.