In previous publications (1) we have called attention to the immunologica significance of the Rh, A, B, M, and N factors for the origin of the erythroblastosis fetalis. We now are wondering whether these bloodfactors might also play a part in other diseases.Gregg (2) has associated several infectious diseases (e.g. rubeola) during the first months of pregnancy with the appearance of congenital malformations of the newborn. Deviations as cataract, deaf-mutism, vitium cordis etc. are usually attributed to the direct action of the noxious agent (virus) upon the rapidly dividing cells, the organism still being in course of development. This opion suggests, that precisely those organs will be affected whose embryonal cellgroups show the greatest activity a t the moment of infection.We doubt, however, whether all clinical deviations which arise in these orubeolachildren)) can be explained by a direct action of the virus. In two cases of children, who showed copious petechial heniorrhages, a remarkable fact was observed in their serological reactions. The serum of the mothers who had suffered from rubeola in the second and third months of pregnancy, showed an abnormally high, either anti-A or anti-B titer. As a hemorrhagic condition of a newborn might be a result of an iso-sensitization of the mother by a certain blood antigen of the fetus, we believed that this possibility should be taken into consideration in these cases. We therefore considered whether in this case the rubeola virus has caused the iso-sensitization of the mother producing immune anti-A or anti-B antibodies, these being responsible for the hemorrhages, the virus only being involved indirectly.A more recent observation made us wonder whether the observed heartdeviations and the congenital heart-anamolies in general (whether or not asso-The Onze Lieve Wrouwe Gasthuis, Amsterdam.