Numerous techniques have been described in the literature to aid the obstetrician in safely and easily performing an intrauterine transfusion. None, however, have addressed themselves to the question of whether the transfused cells actually enter the fetal peritoneal cavity. We have used gray-scale ultrasonography to evaluate this question in 4 patients who had undergone a total of 8 intrauterine transfusions. By scanning the fetal abdomen both before and after the transfusion, we were able to identify the transfused fluid within the fetal abdomen in all cases.