Fetal blood sampling was possible during the third trimester of pregnancy by direct puncture of the umbilical vein near its placental insertion, using a needle guided by ultrasound. Between 2 and 6 ml of pure fetal blood were obtained from three pregnancies without adverse effect on the fetuses. If this new procedure proves to have an acceptable complication rate it should widen the field of prenatal diagnosis for the detection of treatable diseases of the fetus.