Monoamine oxidase (MAO) is linked to psychiatric and neurological disorders, because inhibitors of the enzyme are used clinically for treatment of affective disorders and Parkinson's disease. One of the interesting new aspects of MAO is the occurrence in the human population of deletions of genes coding for one or the other enzyme subtype (A or B). This leads to the possibility of a genetic basis for psychiatric disorders based on MAO. Subjects with deletions of type A or B, and combined deletions, have been described. In the first group of 6 papers in this book, the occurrence and characterization of these phenotypes, as well as the structure of MAO genes, is explored. Advances in the biochemistry of MAO subtypes and their physiological function and localization in brain and periphery is included. Other sections of the book deal with the neuroprotective action of MAO inhibitors and their pharmacology, especially the pharmacology of new MAO-B inhibitors.