In an investigation of 70 chronically mentally ill patients in a district psychiatric hospital, 11 cases were discovered which had been diagnosed up to now as schizophrenia, but could now be diagnosed as being of organic origin. In group 1 (cases 1–6) there are dementive states after toxic, inflammatory or early childhood brain damage and familial epileptic malady with slowly progressive brain atrophy. They were easy to recognize clinically in their organic psychosyndromes, dementia, neurological symptoms and CT findings showing extensive, massive brain damage. In group 2 (cases 7–11), in contrast, there are patients with chronic psychoses of remittent course, with brain findings indicative of centrencephalic damage. On superficial examination they give a schizophrenic picture, but can be differentiated from this by the absence of schizophrenic personality changes and thought disturbances, and also by the form of the hallucinations. These are distinguished by their plastic character, and show the criteria which Schroder had already pointed out 60 years ago for the differentiation of exogenous and endogenous hallucinations.