Although it has been known since 1866 (von Korber) that fetal hemoglobin is more resistant to denaturation by alkaline solutions than adult hemoglobin, it is only in the past few years that the measurement of fetal hemoglobin has been shown to have clinical significance. At birth, the normal full-term infant has 50 to 90% of its hemoglobin in the fetal form,1and during the first two years of life this decreases gradually until the normal level for adults of less than 2% is reached.2In certain pathological conditions, production of large amounts of fetal hemoglobin may continue throughout life, while in others there may be a temporary increase in fetal hemoglobin production. The fact that a newborn infant has a level of fetal hemoglobin much higher than that of its mother makes it possible to identify the source of bleeding occurring during delivery, that is, whether it is