The application of the hydroperoxidase activity of immobilized lipoxygenase to xenobiotic metabolization is reported in this work. Soya bean lipoxygenase has been immobilized by covalent coupling to oxirane acrylic beads. This immobilized system has been applied to the oxidation of chlorpromazine (CPZ), a phenothiazine of wide pharmacological use which in some cases presents toxicity. Immobilized lipoxygenase produces the oxidation of CPZ in the presence of hydrogen peroxide at acidic pH, maintaining a high level of activity and stability. In comparison with free lipoxygenase, the immobilized enzyme system shows higher catalytic efficiency and protection against enzymic inactivation produced by the presence of H(2)O(2). When the system of immobilized enzyme was loaded into a bioreactor operating in continuous mode, the level of CPZ oxidation was higher than obtained using a discontinuous procedure or the free enzyme. The results obtained in this work suggest that a system of covalent immobilized lipoxygenase operating in continuous mode may constitute a valuable tool for xenobiotic detoxification or metabolization studies.