Calcitonin is used in the treatment of osteoporosis and several adverse effects, such as rash, antibody presence, hypocalcemia, etc have been reported with the therapeutic use of large quantities of this hormone. The results found in this paper show that 7 h after administration of large doses of calcitonin to osteoporotic patients on hormone treatment, the acid-base status shifts to metabolic alkalosis. This represents another adverse effect of the use of pharmacological doses of calcitonin.