The author has reviewd papers about heredity diseases and verified that in some of them (target-cell anemia, hereditary hemolytic jaundice, ovalocytic anemia, Biermer's pernicious anemia, constitutional thrombopathia, dystrophia myotcnica (Thomsen's disease and paramyotonia), Friedreich's disease, Charcot-Marie's disease, epilepsy, keratosis follicularis or Darier's disease, brachy-dactyly and gastric cancer) have been described individuals whose behavior with reference to heredity is very similar to the siclemic in sicle cell anemia. These individuals by means of special proofs are identified because they present very early (in some cases congenital) some of the clinical signs of the disease. These observations shows: a) that it is possible to identify the heirs of a pathological condition before the development of the disease and consequently, also the carriers; b) that the presence of identificable carriers is a characteristic of hereditary diseases, perhaps excepting congenital anomalies. They also suggest that the skipping phenomenon should be related with the carriers. It is suggested a census and periodical examinations of these individuals with a view to get some data about the factors responsible for the development of the disease. Perhaps these data might contribute to establish the basis of eventual prophylactic measures against the above mentioned diseases. In Biermer's pernicious anemia the hepathotherapy should be applied to the individuals with gastric achlorhydria, as it it was advised by Askey, as a preventive.