We compared the biochemical effects and safety of pamidronate (30 mg a day for 3 consecutive days) versus clodronate (300 mg a day for 3 consecutive days) via intravenous infusion in 14 patients with Paget's disease of bone (PDB). Both drugs induced a decrease in serum alkaline phosphatase levels as well as the elimination of hydroxyproline from urine, an effect most marked in the group treated with pamidronate. The response was maintained for 6 months after the infusion in the majority of the patients. No relevant side effects were found, except post-infusion febricula and in one patient, self-limiting thrombopenia 6 months after the infusion. We conclude that the intravenous infusion of either of the two drugs may constitute a safe and effective alternative for treatment of PDB with marked biochemical activity or resistant to conventional therapy.