Abstract The cytochalasans, fungal metabolites that interact with actin, can affect lymphocyte proliferation; high concentrations inhibit lectin-induced proliferation and low concentrations augment it. The phorbol ester tumor promoter, PMA, alone is not mitogenic for primary lymphocytes but enhances the activity of mitogenic lectins. Because the cytochalasans have been reported to increase intracellular Ca 2+ and because PMA activates protein kinase C, lymphocytes were treated with PMA and cytochalasin B (CyB) to determine if this combination would induce DNA synthesis. While this treatment by itself did not cause proliferation, lymphocytes cultured with PMA and CyB overnight, washed, and recultured with IL-2 proliferated to the same degree as lymphocytes stimulated with Con A. Three different cytochalasans, cytochalasin B, cytochalasin D, and chaetoglobosin C, all of which bind to cellular actin with different affinities and only one of which affects glucose transport, induced IL-2 receptors in combination with PMA. Flow cytometric analysis with an antibody to the IL-2 receptor a subunit confirmed the induction of receptors on CD8 + cells. However, no IL-2 was produced after the exposure of lymphocytes to the combination of cytochalasans and PMA. Therefore, there was sufficient signal to induce IL-2 receptor expression but not to induce IL-2.