We report a randomized placebo-controlled double-blind study of amino-hydroxybutylidene bisphosphonate (alendronate), infused over 1 h, in 15 patients with Paget's disease of bone. Alendronate, 10 mg/day for 5 days, suppressed urinary hydroxyproline to 44.9 +/- 4.8% and serum alkaline phosphatase to 74.6 +/- 5.4% of their pretreatment values within 1 month of the start of treatment. Within 5 months of the start of treatment serum alkaline phosphatase fell to 47.9 +/- 6.3% of pretreatment values. These effects were associated with a decrease in serum calcium and phosphate and in urinary calcium excretion and with a rise in serum iPTH values. A transient fever was observed in 3 of 10 patients who received alendronate during the course of the infusions, and this was associated with a decrease in the total and differential white cell count. No adverse effects were noted on renal function as judged by glomerular filtration rate and indices of proximal and distal tubular function. This regimen may simplify the management of patients with Paget's disease of bone.