1. A quantitative immunologic technic for the determination of fetal hemoglobin has been developed using a specific anti fetal hemoglobin serum.
2. Fetal hemoglobin occurs in many normal adult individuals in extremely small quantities: values of up to 1.0 per cent of the total hemoglobin may be in the form of the embryonic compound.
3. The alkali-resistant hemoglobin fractions detected by chemical procedures in a number of hematologic diseases are, in all probability, identical with the normally occurring fetal hemoglobin of the red cells of newborn infants. It is suggested, therefore, that these diseases are characterized by abnormal quantities of fetal hemoglobin rather than by an abnormal fetal-like component.