AbstractSoybean lipoxygenase‐1 was covalently coupled to agarose with 75% recovery of catalytic activity. Because evidence was obtained that the immobilization resulted in improved operational stability of the enzyme, a lipoxygenase‐reactor and a continuous process for the synthesis of 13‐hydroperoxy‐linoleic acid and 15‐hydroperoxyarachidonic acid were developed. A procedure based on spectrophotometric hydroperoxide assay and constant oxygraphic monitoring of the effluent is presented for the calibration of the reactor to operate at the highest conversion efficiency when oxygenating quantitatively the substrate. Under these conditions, the reactor was capable of producing about 0.6 mg of hydroperoxy fatty acid/1.0 ml of wet gel/hr. The covalently coupled enzyme has been stable during six months of storage at 3 C in 0.2 M Na‐borate buffer, pH 9.0, and during the same period, its operational stability in the column has been unaltered under the conditions used.