This review reports on aminoaldehyde dehydrogenases (AMADHs, EC 1.2.1.19),     which oxidize ω-aminoaldehydes arising from polyamine degradation. Some of the aminoaldehydes spontaneously cyclize to relatively stable compounds, the others (or their degradation products) are reactive and show considerable cytotoxicity. The main physiological role of the enzyme probably resides in detoxification and stress response. AMADH reaction is NAD(P)-dependent and produces nonproteinogenous amino acids. Molecular and kinetic properties of AMADHs in microorganisms, plants and animals are described. Based on amino acid sequence, AMADHs are homologous to betaine aldehyde dehydrogenases (BADHs, EC 1.2.1.8) and to non-specific aldehyde dehydrogenases (ALDHs, EC 1.2.1.3, 1.2.1.5). The former enzymes participate in the formation of the osmoprotectant glycine betaine and currently they are studied with respect to genetic engineering of plants for increased salt tolerance. The three-dimensional protein structure of a plant AMADH has not yet been analyzed, but it can be modeled using known BADH and ALDH structures as templates. From such a model, a putative catalytic mechanism of AMADH may be deduced. It is obvious that AMADH represents a member of the big protein family of ALDHs with distinct      but partially overlapping substrate specificities. AMADHs are thought to be intracellular enzymes. However, it is still not clear whether in plants they are localized in the cytoplasm, mitochondria, plastids or microbodies. The growing research work on AMADHs and BADHs, which we are witnessing, will further contribute to understanding of protective cellular mechanisms, namely in plant organisms. To point out this, possible future trends in the study of AMADHs are outlined.