This study was designed to measure changes in AFP levels and increases in fetal red cells in maternal blood before and after delivery to detect fetomaternal hemorrhaging in 41 full-term singleton deliveries. Discrepancy was noted between the increase in fetal red cells and the elevation of AFP levels. Six cases (14.6%) showed both elevation of AFP levels and an increase in fetal red cells. Six showed elevation of HbF concentration with stable AFP levels, and another 6 showed an increase in maternal serum AFP levels with stable HbF concentration. The measurements of maternal serum AFP levels seem highly useful for detecting FMH in the presence of fetomaternal blood incompatibility.