For 2 years bone density changes in patients with rheumatoid arthritis were monitored to determine the effect of low dose corticosteroid treatment. Sixteen perimenopausal females were studied. Of these nine were treated with 5 to 20 mg prednisone per day and seven had no steroids. The differential effects on trabecular bone density and on cortical bone in the radius and the tibia were examined with high precision peripheral quantitative computed tomography (QCT). Steroid therapy did not influence cortical bone loss and had only a minor influence on trabecular bone density. Of greater importance was the influence of estrogen depletion. Corticosteroids and estrogen depletion, however, cannot explain fully the yearly loss of 5.7% in the trabecular and 4% in the cortical bone of the radius.