To the Editor: In their recent article in the September 10 issue (“Effects of Prolonged Thyrocalcitonin Administration on Paget's Disease of Bone”), Haddad et al. found no change in urinary excretion of sodium and phosphorus and a transient hypercalciuria in two of the three patients studied. Intramuscular administration may explain the differences between these results and those observed by others.1,2 It is likely that urinary excretion of sodium, calcium and phosphorus increases as long as the level of calcitonin in plasma is sufficient. Thereafter, the homeostatic mechanisms produce a compensatory diminution of the renal excretion of these electrolytes. The amount.