Chromatographic separation of labeled globin chains was performed on peripheral blood of 38 patients with homorygousβ-thalassemia. In 11 patients globin synthesis was also studied in bone-marrow cells. The results showedβ/αsynthetic ratios in the common range ofβ+-thalassemia (from 0.11 to 0.39) in 16 out of 27 Kurdish Jews (59%) and in ten out of 11 Arabs (91%). In nine Kurdish Jews (33%) and in one Arabβd`-thalassemia was found. In a few patients from the latter group a very small peak was detected in theβregion, which co-chromatographed withβ-chains from non-thalassemic individuals, but apparently represents synthesis of a non-globin protein. In two affected siblings, synthesis of small amounts ofβ-chains was demonstrated in peripheral blood (β/α0.018–0.025) and in one sample of bone-marrow cells (β/α0.046). These ratios are lower than any previously reported inβ+-thalassemia. Identification of the presumedβ-peak in these patients was based on an approximate tenfold increase inβ/α,γ/αandδ/αsynthetic ratios measured in hemoglobin isolated by gel filtration. In eight pairs of siblings synthetic ratios were almost identical.β/αandβ/αsynthetic ratios were higher in bone-marrow cells than in peripheral blood. In bone-marrow cellsγ-chain synthesis was lower, often resulting in a more marked chain inbalance (non-αversusα) than in peripheral blood particularly in patients withβd`-thalassemia.