In the past decade, hormonal therapy has been advocated in the palliative management of patients with metastatic breast carcinoma1; reports of temporary palliation have been published from many centers,2and a wide discrepancy between the incidence of subjective and objective improvement has been noted. In a preceding paper,3ait was pointed out that metabolic studies are an important aid in defining the course of malignant disease, in gaging the effect of therapeutic agents, and in studying their mode of action. The mineral metabolism of patients with active osteolysis has been characterized by elevated urinary calcium and phosphorus excretions and negative balances.3At times, excessive rates of demineralization exceed the ability of the kidneys to excrete calcium, resulting in hypercalcemia.3aConversely, patients with osteoblastic metastases have characteristically subnormal urinary calcium excretion and a tendency to maximal calcium retention.4 On occasion, patients with osteolytic metastases may spontaneously