AbstractAutoxidation of pure soybean phosphatidylcholine liposomes at 40 C was found to proceed without an observed induction period, but otherwise, the rates of disappearance of the linoleic acid (70% of total) and linolenic acid (6% of total) followed typical autocatalytic kinetics. Incorporation of 0.05 mol % of tocopherol into the liposomes produced an induction period of about 7 hr under the condition used for the incubation. The produts formed from the autoxidation of pure soybean phosphatidylcholine liposomes were mostly 9‐ and 13‐hydroperoxyoctadecadienoates (isolated as hydroxy esters). The yield of hydroperoxides withcis,trans configuration was about the same as those withtrans,trans configuration throughout incubation period. After extensive autoxidation, a large quantity of trihy droxyoctadecenoate was also produced. When a large quantity of dipalmitoyl phosphatidylcholine was incorporated into soybean phosphatidylcholine liposomes, the rate of autoxidation decreased and was found to conform to apparent first‐order kinetics. In this system, the yield oftrans, trans hydroperoxides was much greater than that ofcis,trans isomers at all stages of autoxidation. Late in the autoxidation of the mixed liposomes, both trihydroxyoctadecenoate and hydroxyepoxyoctadecenoate were produced in substantial quantities.