In view of the claim that low 25-hydroxyvitamin D (25-OHD) concentrations may contribute to the pathogenesis of bone disease in patients with beta thalassaemia major and iron overload, we have assessed the concentrations of 25-OHD, 1 alpha,25 dihydroxyvitamin D (1 alpha,25(OH)2D), parathyroid hormone, and osteocalcin in such patients. 25-OHD concentrations were significantly lower in patients with thalassaemia major and iron overload than in controls and in some patients were subnormal or undetectable. 1 alpha,25(OH)2D concentrations were, however, normal in all patients and were similar to those in controls. Serum parathyroid hormone and plasma calcium concentrations were also normal and not significantly different from those in controls. Although 25-OHD concentrations increased significantly between January and June, there was no change in 1 alpha,25(OH)2D concentrations. 25-OHD concentrations remained lower than control values, even in June. Parathyroid hormone concentrations fell, but not significantly, between January and June, but calcium concentrations did not alter. Osteocalcin concentrations were normal in all patients except one, who had extremely low concentrations of this protein. The concentration of osteocalcin was not related to 25-OHD or 1 alpha,25(OH)2D concentrations. Thus normal calcium homeostasis is maintained in patients with thalassaemia major despite low or low-normal 25-OHD concentrations; this is probably achieved through the maintenance of normal 1 alpha,25(OH)2D concentrations, which were indistinguishable from those in controls. Normal 1 alpha,25(OH)2D, parathyroid hormone, and osteocalcin concentrations argue against an important role for vitamin D deficiency in the pathogenesis of thalassemia bone disease.