75 patients with Paget's disease of bone were treated with a drug combination intended to increase the production of endogenous calcitonin and decrease that of parathyroid hormone. The first regimen of oral calcium, thiazide diuretic, aluminum hydroxide and low-phosphorus diet was given to 41 patients for a mean of 800 days. A simpler regimen of oral calcium and thiazide diuretic was given to 34 patients for a mean of 750 days. There was a similar fall in mean plasma alkaline phosphatase to 71 +/- 24 (SD)% of initial with the first regimen and 72 +/- 17% with the second at 150 days, with a gradual rise after 500 days. Urinary hydroxyproline fell from 165 +/- 111 to 112 +/- 93 mg/day. Plasma calcium rose slightly with both regimens and plasma inorganic phosphorus fell with the first. Serum parathyroid hormone and calcitonin levels were unchanged. Urinary calcium was not changed by the first regimen and rose by 40 +/- 54 mg/24 h with the second. Clinical improvement approximately paralleled biochemical improvement. It is suggested that, in view of its low cost and convenience, this treatment has a place in the management of Paget's disease of bone.