A total of 295 patients with lytic bone metastases from breast cancer were randomized to receive chemotherapy or chemotherapy plus pamidronate (Aredia) 45 mg intravenously every 3 weeks. Primary endpoints were time to progressive bone disease (evaluated by blind extramural review), and improvement in pain (according to a 6-point self-assessment scale). Secondary endpoints included incidence of bone-related complications (pathological fractures, tumor-induced hypercalcemia, need for radiotherapy), sclerotic response of lytic lesions, WHO performance status, and analgesic score. Median time to bone progression was 249 days and 168 days in the pamidronate and control groups respectively (p = 0.02). Marked improvement in bone pain was observed in 44% of patients receiving pamidronate compared to 30% in controls (p = 0.025). With respect to secondary endpoints, pamidronate reduced the need for radiotherapy (66 times vs. 82 times in controls), and median time to radiotherapy was 697 days with pamidronate, 571 in the control arm. No severe adverse reactions or worsening of chemotherapy-induced toxicities were observed during 1598 pamidronate infusions. We conclude that intravenous pamidronate is well tolerated, significantly prolongs time to progressive bone disease, and significantly improves bone pain in patients with osteolytic metastases from breast cancer.