Bryostatin, is an antineoplastic agent with activity in both solid and liquid tumors. When added to tissue culture cells this agent shares a number of similarities with phorbol esters. In this report, we evaluate Bryostatin's effect on human polymorphonuclear leukocytes. Bryostatin stimulates the release of specific granules with a parallel dose response curve to phorbol 12-myristate 13-acetate (PMA), but induces release of superoxide at a significantly slower rate than PMA. Competition experiments demonstrate that Bryostatin, although sharing little structural similarity with PMA, can bind to the PMA receptor. In addition, both Bryostatin and PMA stimulate the phosphorylation of almost identical proteins in intact PMNs. These experiments suggest that Bryostatin may activate PMNs by binding to the PMA receptor, which is currently felt to be the calcium, phospholipid-dependent protein kinase.