A total of 49 cordocenteses, including 40 intrauterine intravascular fetal blood tranasfusions, were performed in 30 pregnancies complicated by red cell isoimmunization. Transfusions were started at 19-33 weeks' gestation and repeated up to five times, at one-to-four week intervals. The volumes of transfused blood were 20-110 ml, hematocrits were 58-82 percent and the rate of transfusions was 1-15 ml/min. The pretransfusion fetal hemoglobins were 3.5-11.6 g/dl and the posttransfusion fetal hemoglobins were 7.5-15.6 g/dl. There were three intrauterine deaths and two neonatal deaths. The overall survival rate was 83.3 percent including all cordocenteses. The survival rate for the intrauterine transfusions was 81 percent.