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Udgivelsesdato: august 2008 The kinetics of the lipid peroxidation reaction is only partly under- stood. Although the set of reactions constituting the overall reaction is believed to be known, it has not been possible to predict how the reaction will respond to a change of one or more of the parameters, e.g. initial concentrations of reactants or different ways of initiating the re- action. Nor has it been possible to predict the time dependence of the products. The reason for these problems is the complicated structure of the kinetic scheme, which includes a chain reaction. In this work we perform an in depth analysis of the importance of the individual reaction steps and we introduce a new quasi-stationary concentration method based on the assumption that one or more concentrations vary much slower than the others. We show that it is justified to use a quasi-stationary concentration approximation for the alkyl radical L· , but not for the peroxyl radicals LO·2 as assumed in previous works. The method allows us to derive manageable analytical expressions. Based on literature values of the rate constants we are able to intro- duce specific simplifications that allow us to obtain simple analytical expressions for the time dependence of all concentrations involved in the process.