In the title for this morning’s session, the term “implications” is quite appropriate, for there is at present no known enzyme that is responsible for the genesis of mental illness. Thus, selecting topics and speakers for this session was rather difficult for Dr. Ho and me, because we did not want “just another” symposium on the biochemistry of mental disease. We decided that the topics for this session should represent not only those areas of interest today, but also those most likely to exert a significant impact on future progress in understanding the biochemistry of mental illness. We selected four areas of research that in our opinion have exciting possibilities. These include the advances in the areas of monoamine oxidase, tyrosine hydroxylase, and the enzymes involved in the transmethylation of the biogenic amines.