The ultimate supreme function of the body is mentation; the other portions of the body are subservient to it. Dysmentation is very common, highly distressing, and enormously expensive. All abnormalities in mentation are presumably associated with altered metabolism. Dysmetabolism causes dysmentation and vice versa. Altered cerebral metabolism is produced by primary or secondary cerebral disorders in the body, and by extracorporeal influences—abnor- malities in diet, climate, social status, and num- erous other environmental factors; there fre- quently is a polycyclic interplay of influences. Dysmentation is often found in many genetic disorders, hyper- and hypoparathyroidism, hy- per- and hypoadrenocorticism, and hypothy- roidism. There are indications that it also occurs frequently in many other endocrine and metab- olic disorders, but data are inadequate. Many neurotransmitters have been described, includ- ing especially acetylcholine, norepinephrine, dopamine and serotonin. Abnormalities in the metabolism of one or more of these have been reported in various types of dysmentation. In mental depression and mania there are ab- normalities in catecholamine metabolism, with lesser changes in serotonin. Certain observations have suggested abnormalities in serotonin me- tabolism in schizophrenia, but data remain in- adequate. Hallucinations and other marked be- havioral changes have accompanied altered serotonin metabolism and/or ingestion of sero- tonin-like compounds. Changes in acetylcholine levels have produced anger, rage, anxiety and other behavioral states. Sleep seems to be as- sociated with increased serotonin and decreased catecholamine levels; insomnia accompanies the reverse. Learning and memory are influenced by the metabolism of protein, nucleotides, carbo- hydrate, fat, vitamins, minerals, and numerous other factors. The brain has richer contents of adenosine-3',5'-phosphate, adenyl cyclase and phosphodiesterase than any other organ, but relatively little is known about the functions there of this nucleotide. As endocrinologists and metabolists, problems of dysmentation con- front us as highly interesting, and probably richly rewarding areas for research, teaching and prac- tice. (J Clin Endocr 31: 461, 1970)