It seems to me proper to stress from the beginning that there are various types of depressions. Often they are ill-defined, while at other times they fit into the clinical entities of manic-depressive reactions or later-life (involutional) groups. In addition, psychoneurotic depressions are also recognized. However, the essential nature of all these types of depressions is still poorly understood. Treatment therefore cannot be based on an aetiological concept or be specific for depression, but must be based on the psychopathological data.