Serum concentrations of T4, T3, rT3, and TSH were measured by radioimmunoassay in 45 patients suffering from beta-thalassaemia. A TRH stimulation test was performed and the binding capacity of TBG and TBPA for T3 and T4 measured by reverse flow zone electrophoresis in a group of these patients. Mean T4 serum concentration was lower in thalassaemic patients than controls; T3, rT3, TSH levels, and the pituitary response to TRH were normal. TBPA binding capacity for thyroxine was greatly decreased, probably due to iron overload impairing the liver function. The decreased circulating total thyroxine might be explained by the reduced TBPA capacity, serum free thyroid hormone concentration total thyroxine might be explained by the reduced TBPA capacity, serum free thyroid hormone concentration values being normal. It is concluded that thalassaemic children are euthyroid, despite often having low-normal or subnormal thyroxine levels.