Calcium balance studies and measurement of 25-hydroxyvitamin D3 (25[OH]D3) levels were performed on a vitamin D intoxicated, hypoparathyroid patient before, during, and after successful management of hypercalcemia with oral prednisone therapy. Prednisone effected a dramatic reduction in both mean serum calcium levels and mean 24-hour urinary calcium excretion within four days on two separate occasions. No changes were apparent in fecal calcium excretion. Calcium balance became less negative with prednisone treatment. Levels of 25(OH) D3 during the same period did not change. Decreased calcium mobilization from bone best accounted for the glucocorticoid-mediated amelioration of hypercalcemia.