Oxidative stress, which is characterized as dysbalance between free radicals and antioxidants in favour of radicals, participates in the pathogenesis of many diseases and their complications. Carbonyl stress is closely related to oxidative stress and is described as increase of reactive carbonyl compounds caused by their increased formation or decreased degradation and clearance. Both oxidative and carbonyl stresses cause damage to proteins--they lead to formation of advanced oxidation protein products--AOPP, advanced glycation end-products--AGEs and advanced lipoperoxidation end-products--ALEs. These compounds have several biological effects--e.g. stimulation of secretion of cytokines, adhesive molecules and growth factors and take part in the development of complications of diabetes mellitus and chronic renal failure.