The efficacy of five therapeutic regimens using (3-amino-1-hydroxypropylidene)-1,1- bisphosphonate (APD or pamidronate) was assessed in patients with Paget's disease of bone. These regimens were as follows: (a) pamidronate 600 mg/day given orally during six months; (b) iv infusion of 20 mg daily for 10 days; (c) iv infusion of 40 mg daily for 5 days; (d) iv infusion of 10 mg daily for 4 days and (e) a single iv infusion of 10 mg. Six months after the initiation of therapy, urinary excretion of hydroxyproline and serum alkaline phosphatase activity (expressed as percent of their initial value) were: Group a: 30 +/- 10 (mean +/- SE) and 30 +/- 6, Group b: 55 +/- 8 and 46 +/- 6, Group c: 54 +/- 7 and 57 +/- 6, Group d: 53 +/- 7 and 69 +/- 4, and Group e: 85 +/- 10 and 98 +/- 4 respectively. Oral route was accompanied by digestive intolerance. On the contrary, except for rare and transient "flu-like syndromes", the iv treatment was not associated with any serious secondary effect. Intravenous infusion of pamidronate, 20 mg for 10 days or 40 mg for 5 days, appears as an interesting alternative to the oral route in the treatment of Paget's disease of bone.