The question has been addressed whether the side chain contributes to the antioxidant activity of Ubiquinones. The length, the chemical composition and structure of the chain have been considered. The effect of the actual concentration of the quinone in egg lecithin vesicles has been investigated by means of both UV spectroscopy and time resolved fluorescence quenching experiments of 12-AS. The results indicate that the antioxidant properties of the quinone do not seem to depend on the side chain.