There is uncertainty about the best treatment for steroid-induced osteoporosis. Thirty-six patients with steroid-dependent, chronic obstructive lung disease and associated steroid osteoporosis have been studied, of whom 18 were treated with salmon calcitonin and the other 18 served as controls. Treatment lasted for 6 months and consisted of 100 I.U.s.c. every other day. In the controls there were significant decrements of 1.4% and 3.5%, respectively, in cortical and cortical and trabecular bone mineral content, whereas in subjects on calcitonin there were increments of 2.6% and 2.7%, respectively. Additional evidence of positive effect of calcitonin was derived from the reduced incidence of new fractures occurring during the observation period. A significant reduction in back pain was a further consequence of the hormone therapy.