A case of anemia caused by loss of fetal blood into the maternal circulation is reported. The diagnosis was established by detection of fetal erythrocytes in the maternal circulation by differential agglutination. Ashby counts on the mother's blood, showed that the fetal cells persisted in the maternal circulation for approximately 80 days, following which the mother developed Rh antibodies. Fetal hemorrhage from the placenta probably not infrequently causes anemia in the newborn period. In many cases, however, conclusive proof of such a diagnosis is not made.