Growth retardation is a clinical feature of patients with thalassemia major, and endocrine studies have frequently revealed the presence of normal growth hormone (GH) secretion. The present study was undertaken in 14 prepubertal thalassemic children (9 males and 5 females), aged 2(2/12) to 10(3/12) years, with the aim of evaluating GH response to i.v. arginine, oral L-dopa stimulation and insulin-like growth factor-1 (IGF-1) levels. Eleven patients had peak serum GH levels less than 7 ng/ml and two patients had peak serum GH levels of 7-10 ng/ml with arginine. Similarly, 10 patients had peak levels less than 7 ng/ml and one patient had a peak level of 7-10 ng/ml with L-dopa. Thus, nine of the patients had GH deficiency and two had partial GH deficiency. Three patients had elevated basal GH values. The serum IGF-1 levels in the patients were not statistically different from the levels in the controls, but three patients had low IGF-1 values. These findings suggest a defect in the regulatory mechanisms of GH secretion.