Increased production of HbF can be considered a marker for hypoxemia, since increased levels of HbF synthesis have been found in newborn infants following maternal hypoxemia, placental insufficiency, and diabetes, as well as in infants with broncho-pulmonary dysplasia and children with congenital cyanotic heart disease. To examine if a quantitative relationship exists between the mRNAs encoding globins and their translation into proteins during hypoxemic erythropoietic stress, the relative amounts of the mRNAs and the relative amounts of the α,β,γ-globin synthesis in samples obtained from cord blood from infants of insulin-dependent diabetic mothers, intrauterine growth-retarded infants of preeclamptic mothers and older infants with cyanotic heart disease were measured and compared. The synthesis of globins in reticulocytes was measured by the incorporation of [3H]-leucine followed by the separation and quantitation of the polypeptides on a C4-reverse phase HPLC. The relative proportions of the mRNAs of globins were determined by RNase protection assay. Total RNA isolated from blood (50μl) was incubated with [32P]-labelled cRNA probes ofα,β,γ-globins, followed by RNase A/T1 digestion, separation of the protected fragments and densitometry of the radioactive bands by phosphorimaging. The study population showed an increase in HbF synthesis, compared to controls. There was a strong correlation (r2=0.993; n=16) between the ratio of mRNAs encoding HbF and HbA and the ratio of de novo synthesis of HbF and HbA. Therefore, under conditions of stress erythropoiesis there is a close correlation between quantitation of globin mRNAs and HbF& HbA synthesis. As well, globin mRNA quantitation could replace the usual method of HbA & HbF synthesis determination.