Pathogenesis of many diseases and their complications is linked to oxidative stress. In the last two years, the attention has been paid also to carbonyl stress which is alosely related to oxidative stress. Carbonyl stress is characterized as an increase of reactive carbonyl compounds caused by their increased formation and/or decreased breakdown and excretion. Reactive carbonyl compounds can be formed from carbohydrates, lipids and amino acids both by oxidative and non-oxidative pathways, can be detoxified by several enzymes and excreated by kidneys depending on their function. Carbonyl compounds can form advanced glycation end-products (AGEs) and advanced lipoperoxidation end-products (ALEs), which are known to take part in the pathogenesis mainly of diabetic and uremic complications.