Superoxide dismutase (SOD) taken in minor concentrations (a few U/ml) displays a pronounced inhibiting effect on the chain oxidation of methyl linoleate and methyl linolenate (but not methyl oleate) induced by 2,2'-azobis(2-amidinopropan) dihydrochloride (AAPH) in micellar solutions of sodium dodecyl sulfate and Triton X-100 in phosphate buffer, pH 7.40, at 37.0 degrees C. The inhibition is evidently caused by purging the system from O(2)*(-). The latter suggests the formation of O(2)*(-) (HO(2)* in the course of peroxidation, most likely, via beta-decay of lipid peroxy radical (LO(2)*. Thermodynamic estimations verify a rather high probability of beta-decay of LO(2)* produced from polyunsaturated fatty acids by contrast to that produced from saturated and monoenic fatty acids. It is speculated that O(2)*(-) (HO(2)*, being an amphiphilic, reactive and highly mobile species, participates in intermicellar (interliposomal) transfer of free valence during lipid peroxidation in microheterogeneous systems.