1. Plasma levels of immunoreactive calcitonin were measured in 22 patients with untreated Paget's disease of bone and in 22 control subjects matched for age and sex.
2. No significant differences in plasma calcitonin were found between patients and control subjects, and hormone levels did not correlate significantly with activity of plasma alkaline phosphatase.
3. These results suggest that Paget's disease of bone is not due to deficient secretion of endogenous calcitonin.