Previous changes of the Psychobiologic unit have been restricted by the timing of each revision. This revision is perfectly timed to include the experiences of psychiatrists of World War II, the results of several years usage by the military and Veterans Administration of a revised army nomenclature, the pattern of a new international code and the results of several years deliberation of the Nomenclature Committee of the American Psychiatric Association. As a result of all these we were enabled to offer a completely new classification in conformity with newer scientific and clinical knowledge, simpler in structure, easier to use and virtually identical with other national and international nomenclatures.