We have undertaken a study of 24 hypercalcemic patients with the use of salmon calcitonin as a therapeutic agent. Seventy-five percent of the patients exhibited a clinically significant decrease in serum calcium and approximately half became normocalcemic within 2 hr. Throughout salmon calcitonin administration, the mean serum calcium of the patients was lower than the pretreatment values. Although the drug did not always lower the calcium level to normal, it often brought the hypercalcemia to more tolerable levels. During the course of calcitonin therapy, the number of patients with normal or near-normal serum calcium ranged from 31.3% (at 96 hr) to 82.4% (at 30 hr). Many of the patients improved symptomatically. The only significant side effects were nausea and vomiting in 12.5% of the patients, which necessitated cessation of therapy in only one. The drug was well tolerated in patients with azotemia. Calcitonin-induced hypocalcemia was not encountered. Salmon calcitonin can be used safely alone or in conjunction with other hypocalcemic therapies.