Activation of T-lymphocytes by antigen, mitogenic lectins, or antibodies against the T-cell receptor complex, particularly in the presence of IL1, induces the secretion ofthe T-cell growth factor IL2. IL2 then has a major role in regulating the duration and magnitude of the immune response. Interaction of antigen, antibodies against the T-cell receptor complex, or mitogenic lectins with T-lymphocytes also induces hydrolysis of membrane phospholipids, leading to the production of diacylglycerol, an activator of the Ca2+-and phospholipid-dependent phosphotransferase, protein kinase C (PKC). Phorbol esters, potent activators of PKC, augment secretion of the T-cell growth factor, interleukin 2 (IL2). Activation of PKC may therefore serve as an important early event in the production and secretion of IL2. We have determined whether IL2 secretion can be induced in the murine cell T-lymphocyte line LBKM 331A5, where PKC is inhibited by staurosporine or sphingosine or in cells where PKC is depleted by prolonged incubation with high concentrations of phorbol esters. In cell5 in which PKC was either inhibited or depleted, antibodies against the T3 portion of the T-cell receptor complex and the mitogenic lectin phytohemagglutinin (PHA) still triggered IL2 secrelion. In addition, the monokine IL1 augmented this ILZ secretion irrespective of whether PKC was inhibited or depleted. These data indicate that activation of PKC is not an obligatory step for IL2 secretion in LBRM 331A5 murine T-lymphocytes.