This article deals with the following problem: to what extent is it possible to draw conclusions about the type of psychosis involved--in a case of endogenous psychosis--when one only has indications about the family background and the development of the personality before the illness, excluding all data about cases in the family, former pathological episodes and the present illness of the patient? Only pure forms of endogenous psychoses have been taken into consideration. Our hypothesis was that schizophrenics show before their illness schizoid features, subjects with an endogenous depression show features of the melancholic type, whilst manic depressives do not correspond to any of these types. After having studied most of the literature on this subject, we have attempted to draw from case histories the most marked features of personality and to obtain an overall picture of the primary personality of schizophrenic, depressive and manic depressive patients. This material was used for a "blind diagnosis" from 40 case histories (20 schizophrenics, 10 depressives and 10 manic depressive patients treated at the Max Planck Institute of Psychiatry, Munich). The results of this evaluation were significantly superior to those of a random distribution. Furthermore, we have attempted to outline the principal elements of the personality of future manic depressives from three examples out of the ten case histories studied. We came to the conclusion that although it is impossible to clearly oppose the primary personality of manic depressives to that of depressive patients, we have found a series of differences that prevent us from outlining a real common denominator for patients with "affective psychoses'.