In systemic lupus erythematosus (SLE) patients, the production of interleukin-2 (IL-2) by blood T lymphocytes in response to stimulation with phytohemagglutinin (PHA) either alone or with phorbol myristate acetate (PMA) or ionomycin, a Ca2+ ionophore, was examined. Deficiency in PHA-stimulated IL-2 production by cells from SLE patients was repaired by the addition of PMA, but not ionomycin. PMA alone did not stimulate IL-2 production but, in concert with PHA, induced IL-2 synthesis. Moreover, PMA was effective in the repair of the deficiency of PHA-induced IL-2 production by both T4+ and T8+ subsets. Thus, for effective IL-2 production, SLE T cells required signals either distinct from or in addition to those supplied by PHA.