Isoprostanes are a newly discovered class of compounds formed in vivo as a consequence of non-enzymatic oxidation of polyunsaturated fatty acids. The isoprostanes produced by free radical-catalyzed peroxidation of arachidonic acid, so called F2-isoP, were the first to be introduced by Mihelich. The discovery of isoprostanes has important evidences for medicine. Their occurrence has been established as the most predictable marker of oxidative stress, while the measurement of their concentration in biological samples is the most recommended approach to the assessment of redox status in vivo, providing a crucial tool to explore the role of oxidative processes in the pathogenesis of human disease.