Since January,1979, we examined all pregnant women visiting our hospital on antierythrocyte unexpected antibodies in order to detect haemolytic disorder in the newborn (HDN) as early as possible. Among the 4,748 pregnant women examined, antibodies could be found in 147 cases (3.1%). Anti-Le antibodies were found to be the most frequent, and anti-E formed the majority of anti-Rh antibodies detected. Blood transfusion seemed to play a great role in the production of anti-E in our examined women. Among the seven Rh (E) incompatible pregnant cases at our hospital, two were so severe as to need exchange transfusion therapy. Therefore, trials were made; i. e. Rh (E)-negative red blood cell preparations were transfused into the same-blood-type women under forty years of age requiring blood transfusion. We had to prepare 6.9 units of Rh (E)-negative red blood cell preparations per day. The amount was within the capacity of our transfusion unit. Therefore, Rh (E)-negative red blood cell preparations should be used for blood transfusion into Rh (E) -negative women under forty years of age who may experience future pregnancy. Moreover, not only anti-Rh (D) immunoglobulin preparations, but anti-Rh (E) preparations should be developed, particularly in Japan.