The effect of i.v. infusions with salmon calcitonin was evaluated in the treatment of acute hypercalcemia in 12 patients. Clinical improvement and a less critical level of serum calcium were achieved within 24 hours for eight of the patients, for another two after treatment for 48 hours. In malignant conditions (six patients) calcitonin was less effective, which could be evaluated within 24 hours. In addition to rehydration, the rapid onset of action and the lack of side-effects make calcitonin a drug of first choice in the treatment of acute hypercalcemia.