Quantitative determinations of anti‐D in sera and amniotic fluids were performed simultaneously in 63 pregnant Rh‐immunized women with Rh‐positive foetuses. It was demonstrated that the ratio of serum antibody to amniotic fluid antibody as a rule is the same. A quantitative analysis of the serum antibody enabled us to identify the foetuses with good prognoses. For ths remaining cases, it was possible to distinguish between moderate to severe cases and very severe cases of erythroblastosis by determining also the concentration or titre of amniotic fluid antibody. Where specimens were taken less than a fortnight before birth, the titre values alone made it possible to prognosticate correctly in 80% cases. Correlation of amniotic fluid antibody and bilirubin levels led to correct prognoses in 92% of the cases. With this background a plan for the control of pregnant Rh‐immunized women is suggested.