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—abnormalities in diet, climate, social status, and numerous other environmental factors; there frequently is a polycyclic interplay of influences. Dysmentation is often found in many genetic disorders, hyper- and hypoparathyroidism, hyper- and hypoadrenocorticism, and hypothyroidism. There are indications that it also occurs frequently in many other endocrine and metabolic disorders, but data are inadequate. Many neurotransmitters have been described, including 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 abnormalities in catecholamine metabolism, with lesser changes in serotonin. Certain observations have suggested abnormalities in serotonin metabolism in schizophrenia, but data remain inadequate. Hallucinations and other marked behavioral changes have accompanied altered serotonin metabolism and/or ingestion of serotonin-like compounds. Changes in acetylcholine levels have produced anger, rage, anxiety and other behavioral states. Sleep seems to be associated with increased serotonin and decreased catecholamine levels; insomnia accompanies the reverse. Learning and memory are influenced by the metabolism of protein, nucleotides, carbohydrate, 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 confront us as highly interesting, and probably richly rewarding areas for research, teaching and practice.