OBJECTIVE To evaluate the change in fetal serum bilirubin levels in response to intrauterine transfusion for red cell alloimmunization. METHODS The records of 37 patients who underwent more than one intrauterine transfusion were reviewed. The following indices were extracted: pre- and post-transfusion fetal hematocrit, total and direct serum bilirubin, reticulocyte count, Kleihauer-Betke test results, volumes of intravascular and intraperitoneal transfusions, and the source used for transfusion. The data were compared for interval 1 (transfusion 1 to 2) and interval 2 (transfusion 2 to 3). The rates of change in bilirubin, reticulocyte count, and percent fetal cells on the Kleihauer-Betke test were defined as the differences between the initial values of one transfusion and the initial values of the next transfusion divided by the number of days between transfusions. Analysis of variance, sign-rank test, and linear regression analysis were used when appropriate. P < .05 was significant. RESULTS The median number of intrauterine transfusions for each patient was 3 (range 2-8). Gestational ages ranged from 22 to 37 weeks. Total bilirubin remained above the 97.5 percentile for gestational age in all but five patients. There was a significant decrease in reticulocyte count and fetal cells on the Kleihauer-Betke test, and an increase in hematocrit with serial intrauterine transfusions. Bilirubin increased significantly after the first intrauterine transfusion (3.9 versus 5.0 mg/dL) and remained elevated thereafter. CONCLUSIONS Fetal total serum bilirubin remains elevated with repeated intrauterine transfusions in fetal alloimmunization. Total bilirubin should not be used to evaluate fetal hematologic responses to the transfusions.