Oxidation of arachidonic acid ethanolamide (anandamide) and eicosapentaenoic acid ethanolamide by soybean 15-lipoxygenase was studied by UV spectroscopy. The KM values for both amides (3.2 and 4.9 μM, respectively) proved to be similar to that for arachidonic acid. Products of double lipoxygenase oxidation were identified in the reaction mixture at an enzyme-substrate ratio of 500 : 1.