In order to clarify whether the damage in gonadotropin secretion due to iron overload in patients with β-thalassemia is of pituitary or hypothalamic origin, 14 euthyroid patients (8 females and 6 males, age 15-24 years) affected by β-thalassemia major with hypogonadotropic hypogonadism were studied. Luteinizing-hormone (LH), follicle-stimulating hormone (FSH) and free α-subunit (FAS) were measured during LH-releasing hormone (LH-RH) stimulation test, and thyroid-stimulating hormone (TSH), prolactin (PRL) and FAS during thyrotropin-releasing hormone (TRH) stimulation test. During LH-RH stimulation, the mean basal LH, FSH and FAS levels were similar to those found in normal prepubertal children, but the peak values were lower than those found in such children. Also during TRH stimulation, the mean peak values of FAS were lower than those of normal prepubertal children, but the TSH response was normal. The lack of response of gonadotropins and FAS to LH-RH cannot exclude hypothalamic failure; however, the normal response of TSH to TRH, in spite of the poor response of FAS, indicates that the origin of hypogonadotropic hypogonadism is the pituitary damage concerning not only the gonadotroph but also the thyrotroph cells.