Taxol (paclitaxel) is a chemotherapeutic diterpene with promising anticancer activity that blocks cell division by preventing microtubule depolymerization. Furthermore, recent studies have shown that taxol has other intracellular effects that may contribute to its effect, particularly in macrophages. The signal transduction mechanisms by which taxol stimulates macrophages to anticancer activity are not clear. The purpose of this study was to determine the effect of taxol on chemiluminescence (an indicator of the production of free radicals) of neutrophils, macrophages and murine macrophage J.774.2 cells. The chemiluminescence was measured in the presence of taxol andór phorbol myristate acetate (PMA) as a stimulant. Taxol stimulated chemiluminescence (without PMA) of neutrophils and macrophages but not of J.774.2 cells, and modulated chemiluminescence of the cells stimulated with PMA.