Fourteen patients with multiple myeloma have been treated with phosphate supplements given orally or intravenously. In all of the seven patients with hypercalcemia, serum calcium was reduced into the normal range and maintained at that level as long as phosphate supplementation was continued. Hypercalciuria was likewise reduced by administration of phosphate, even in the absence of hypercalcemia. All patients experienced some relief of pain, and five became symptom-free. No significant complications of phosphate supplementation were observed.