To determine the frequency of maternal-fetal hemorrhage at or above 1 μl of maternal whole blood. Methods: Seventy-three mothers whose red blood cells bore an Rh antigen (Rh D, Rh c, Rh E) that was absent on red blood cells of their newborns were identified and a new cytological method, the Kleihauerimmunogold- silver-staining technique, was applied on the blood of their neonates to detect and quantify maternal red blood cells. Stringent precautions were taken to avoid contaminations of neonatal blood samples by adult red blood cells. Results: Maternal red blood cells were present in 3 newborns, a frequency of 4% (95% Cl: 1-11%), and the estimated volumes of hemorrhage were 0.8, 1.5, and 101 μl of maternal whole blood. No obstetric factor was clearly associated in this limited study with the occurrence of maternal-fetal hemorrhage. Conclusions: Mother-to-fetus microtransfusion greater than 1 μl is infrequent at or near delivery, and it may be observed after an uncomplicated pregnancy and vaginal delivery.