The Author studies the etiological diagnosis in patients who, showing light somatic disorders (not enough to bring out proper somatic or psychic impairment), have symptoms psychogenic in their appearance, "understood" (Jaspers) and due to hard situations. Discussion is made if there are psychic signs able to point the exogenous factor. The Author claims for Hoche, Kleist, Bonhoeffer, Stertz and Kurt Schneider; he agree with Schneider views, that the only right exogenous sign is impairment in consciousness, even though this sign has its value when the exogenous factor is marked. In exogenous-psychogenic reaction, the primary sign (Stertz's basical sign) together with both the exogenous and evidence of accessory factor in relation to psychic complication, the Author set forth Stertz views that both may appear according to the amount of the exogenous factor, its duration, incidence of definite lesions and convergence of genotypical traits. Four cases are reported: 1 - A man whose wife has tuberculous cachexia. He exhibits agitated depression which could be explained by the lost he would soon experience. However, on physical examination there appeared signs of dementia paralytica, confirmed by changes in the cerebrospinal fluid. He had been healed under malaria even though his wife died in the course of his treatment. This case clears up the value of exogenous-psychogenic factor. 2 - A case of alcoholic delusion in reactional neurosis. After healing the toxic process, remained the conflicts of his former personality. This clear up how in a syndrome one can share the psychogenic nature of a symptom from the exogenous nature of the other (Birnbaum's structural analysis). 3 - In a jealousy delusion of a hypertensive patient, one can find the exogenous and psychogenic factors. In this case, a study is made on the way the exogenous factor aided to worsen the abnormal personality traits. 4 - A case of "abnormal drunkenness" in which Kolle would point to the toxic factor as "not enough". The psychogenic set does not lead to "abnormal drunkenness" but drive it, as may be seen in this case. The Author quotes Heitor Carrilho, who noted 22,33 per cent of cerebrospinal fluid changes for syphilis over 600 patients without clear exogenous symptoms. Many of these cases would perhaps be among those of the exogenous-psychogenic group (completion would allow the psychogenic power to less the resistance of tendencies to crime). This paper introduces to Brasil Kurt Schneider's concept of Hintergrundreaktion, or as it may be said, Background reaction.