Serum levels of soluble Interleukine-2 Receptor (sIL-2R) were investigated in 46 transfusion-dependent Thalassemia Major patients (TM). The values were statistically higher in patients than in normal controls and well correlated with transfusion requirement. In order to identify the peripheral cell population responsible for the high sIL-2R released, we measured sIL-2R levels in the supernates of both unstimulated and lectin-activated peripheral monocytes, T and non-T lymphocytes. Data suggest that T lymphocytes appear to be the major source of the high serum level of sIL-2R in TM.