The bone mineral content of the radius in 37 patients with systemic sclerosis was measured with Americium241 photon absorptiometry. The content was found reduced (p less than 0.05) in patients with systemic sclerosis compared with a group of healthy controls matched for age and sex. Analyses of calcium 'total', calcium ion, phosphate and the parathyroid hormone level in the serum, and the excretion of calcium and phosphate in the urine all proved normal. It is discussed whether the reduced bone mineral content in systemic sclerosis may be an effect of the immobilization of the hands affected by the disease.