The amniotic fluids of 7 pregnant women with Rh-isoimmunization were examined. On the basis of the data of this investigation as well as of the clinical and ultrasound data intrauterine blood transfusions were made in fetuses--from 4 to 8 in number. Forty two spectrophotometric analyses were made in all, but the amniotic fluids were examined before intrauterine blood transfusions as well as before the performance of each subsequent blood transfusion. The authors found changes in the characteristic of the amniotic fluid after intrauterine blood transfusion, which were manifested by the fact that the pigment peak of delta 450 nm was reduced, but the peak of delta 410 nm was increased. In connection with these findings after intrauterine blood transfusions delta 450 nm lost its diagnostic and prognostic value. delta 410 nm before intrauterine blood transfusions manifested gravity of fetal hemolytic disease. After intrauterine blood transfusions its increase was due to blood transfusions and accumulation of methemoglobin in the amniotic fluid.