From reaction mixtures of reducing sugars with primary and secondary amines many heterocyclic and carbocyclic compounds have been separated. From the structures of these substances together with the knowledge about reactive intermediates some degradation pathways can be proposed. Caused by the nature of the sugar (pentose, mono- or disaccharide) and the amine (primary or secondary) differences in the pathways are observed. An attempt is made to present some reactions with emphasis to the Maillard reaction in mammalians.