Manganese poisoning is discussed as being a clinical model in the study of extrapyramidal disorders. Various technical developments are mentioned which have extended our capabilities for investigating the metabolism of Mn. Some observations are presented on the normal physiology of this element and on some distortions thereof. The high concentration of Mn in malanin granules was noted. These bodies were proposed as possibly reflecting chemical and physical changes underlying some extrapyramidal diseases including Mn poisoning. (auth)