1. Four patients with active Paget's disease were given acute injections of a synthetic calcitonin. The calcium lowering effect of human and porcine calcitonin was compared in two patients, and the human and salmon hormone in the other two patients.
2. All three hormones were effective in lowering the plasma calcium, but weight for weight salmon calcitonin was the most potent. Thus salmon calcitonin produced approximately the same effect as a ten times greater dose of human calcitonin. However, porcine calcitonin was the least potent, and compared with human calcitonin, required an approximately tenfold dose for a similar response.