Abstract
BFU‐E from the blood of 14 normal adults have been grown by the plasma clot technique. The hemoglobins synthesized in burst colonies were purified from other proteins by affinity chromatography on Sepharose‐haptoglobin. The radioactivity incorporated in the globin chains was estimated by CM‐cellulose chromatography in urea. The number of bursts scored at the 14th day of culture fluctuated between 50‐130 (average 86, s: 29) for 10^6^ mononuclear plated cells. A constant reactivation of fetal hemoglobin was found (from 1.4% to 11%, mean value 5.8%, s: 3.07), but was lower than previously described, mainly because of the highly selective purification of Hb. This reactivation of fetal hemoglobin was not dependent upon the concentration of erythropoietin (from 1 U/ml to 6 U/ml) nor on the purity of the erythropoietin preparations (from 6 U/mg of protein to 70 000U/mg of protein). In addition, the same subject exhibited a constant proportion of Hb F synthesized in culture over a period of time up to 6 months. A positive correlation exists between the proportion of Hb F in culture and that of F cells present in the blood, with the exception of two subjects. Such findings suggest that Hb F in culture is a characteristic of each individual and that this reactivation often represents an amplification of the Hb F synthesis in vivo.