Oxidation of biological prenylquinols, like plastoquinol-9 (PQH2-9), ubiquinol-10 (UQH2-10), reduced vitamins K1(VK1H2) and K2(VK2H2),α-tocopherol quinol (α-TQH2) andα-tocopherol (α-T) was followed by their fluorescence during sonication of egg yolk lecithin/prenylquinol liposomes. The order of magnitude of oxidation of the prenylquinols by free radicals generated during sonication wasVK2H2VK1H2α-TQH2α-T. It was shown that egg yolk lecithin undergoes degradation even when sonicated briefly under atmosphere of nitrogen and at 0°C. A kinetic study of free radical scavenging action of the prenylquinols in solvents of different polarity was performed. The pseudo-first-order rate constants, k, for the reaction of the prenylquinols with 1,1-diphenyl-2-picryl-hydrazyl (DPPH) in hexane showed that their scavenging activity changes in the order