The distinction between schizophrenic and affective illnesses has been one of the cornerstones of psychiatric classification ever since Kraepelin introduced the twin concepts of dementia praecox and manic depressive psychosis at the turn of the century. It has also long been recognized that some patients have both schizophrenic and affective symptoms, and various interpretations have been placed on these mixed states. To some continental psychiatrists they constitute a third group of psychoses distinct from both schizophrenia and manic-depressive psychosis—the degeneration psychoses of Kleist or the cycloid psychoses of Leonhard. By others they are regarded as genuine mixed states, with the implication that elements of both schizophrenia and manic depressive illnesses are contributing, perhaps because the genetic or constitutional endowment is mixed, perhaps because two alternative defence mechanisms are being utilized simultaneously. Often, however, mixed symptomatology is simply ignored, either by discounting the schizophrenic symptoms and focusing attention on the mood change, or, as most American psychiatrists do, by glossing over the affective symptoms and regarding the illness as a form of schizophrenia differing in no significant respect from other schizophrenias.