THE future of the blood-transfusion services has been the subject of much anxious thought among those who have helped to create and man them and also among the general public. One important aspect of their future is discussed in a leading article in the Lancet (112, July 28, 1945). This is the possibility that Rh-positive blood may be transfused into an Rh-negative individual. The first transfusion of the Rh-positive blood causes the development of anti-Rh agglutinins in the serum, so that a subsequent transfusion of Rh-positive blood may produce an incompatibility reaction exactly similar to that which occurs when Group A blood is transfused into a Group B person, namely, hæmolysis of the incompatible blood cells and possibly jaundice or hæmoglobinuria. This reaction may be mild, severe or even fatal. Further, an Rh-negative woman may have been sensitized by having an Rh-positive baby, or by a transfusion of Rh-positive blood; if she then has an Rh-positive child, there is increased risk of erythroblastosis or of an allied condition in this child. Also, if an Rh-negative mother has an Rh-positive child and is sensitized by this child, her first transfusion of Rh-positive blood may cause an incompatibility reaction. American work has shown that this Rh-sensitivity may last for eight to twenty-two years. In addition to this, anti-Rh agglutinins cannot yet be always detected in the blood. R. R. A. Coombs, R. E. Mourant and R. R. Race have, however (Lancet, 15, July 7, 1945), described a new method of detecting weak and 'incomplete' Rh agglutinins in the blood (cf. also Coombs, R. R. A., and Race, R. R., Nature, 156, 233 (1945) and the discussions by A. J. McCall and S. Holdsworth in Nature, 155, 788 (1945) of hæmolytic disease of the newborn due to the antibody St, H. S. Baar (ibid., 789) on the Race–Wiener test in hæmolytic disease of the new-born, and G. Plaut, M. Barrow and J. M. Abbott (Brit. Med. J., 273, Sept. 1, 1945)).