This study analyzes the serum transferrin receptor (sTfR) levels in a series of 184 ex-thalassemic patients with a follow-up of 1 to 9 years after bone marrow transplantation (BMT) for homozygous beta thalassemia. A significant inverse correlation between sTfR and Hb levels was observed (r = -0.36, p < 0.001). Patients who received the marrow from an HLA-identical sibling donor heterozygous for beta thalassemia displayed significantly higher levels of sTfR than patients transplanted from a normal sibling donor (p < 0.001). A cut-off value of 2600 ng/mL of sTfR was established. Only 3 out of 56 (5%) patients who received the marrow from a normal sibling, reached a sTfR value above the cut-off level, while 64 out of 128 (50%) patients transplanted from a heterozygous sibling donor showed sTfR values > 2600 ng/mL (p < 0.001). These results suggest that the level of sTfR helps to identify ex-thalassemic patients with enhanced or normal erythropoietic activity among those transplanted from HLA-identical sibling donors heterozygous for beta thalassemia. The physiologic and clinical significance of different patterns of sTfR levels in ex-thalassemic patients with beta thalassemia trait deserves to be investigated.