Increased levels of transferrin receptors (TfR) and soluble TfR (sTfR) are reliable indicators of iron deficiency anemia and conditions with enhanced erythropoietic activity. In this study we measured sTfR levels in the cases of beta-thalassemia trait (betaTT) and IDA to see whether it would be a diagnostic tool for the differentiation of betaTT and IDA. On the other hand STfR levels could give an idea about erythropoietic activity in betaTT. Serum transferrin receptor (sTfR) levels were measured with enzyme immune assay in 37 cases with betaTT, in 26 patients with iron deficiency anemia (IDA), in 17 patients with the coexistence of betaTT with IDA, and in 21 healthy controls. Mean sTfR in betaTT (6.54 +/- 1.88) were statistically higher than in controls (5.09 +/- 0.76) and lower than in IDA (11.46 +/- 5.03) and in IDA coexistence with betaTT (14.44 +/- 5.3, p < 0.05 in each comparison). However, in 17 cases with betaTT sTfR levels showed an overlap between the patients with IDA, and in 15 cases with betaTT it also showed an overlap with controls. The finding of higher sTfR levels in betaTT compared with controls suggested that there was a degree of ineffective hematopoiesis in betaTT. Although sTfR levels in IDA were higher than in betaTT, because of largely overlapping values in both groups, it was not satisfactory to distinguish betaTT from IDA.