Quantitative computed tomography (QCT) was used to assess trabecular bone mineral concentration in the vertebrae of 132 children, 45 with suspected disorder of bone mineralisation, 54 with thalassaemia and 37 controls. The range for bone mineral concentration in controls, expressed as equivalent K2HPO4 concentrations, was 90-190 mg cm-3. Abnormally low values were seen in all untreated children with idiopathic juvenile osteoporosis, 3/9 steroid recipients, and three patients with osteogenesis imperfecta. Abnormally high values were seen in 10/14 chronic renal failure patients. Comparison of the single and dual-energy methods showed that the single energy method, which has a lower radiation dose and is less prone to error from movement artifact, is satisfactory in most paediatric applications.