Abstract：We investigated the effect of a single subcutaneous dose of zoledronic acid on particle-induced osteolysis and observed excessive regional new bone formation. We utilized the murine calvarial osteolysis model and polyethylene particles in C57BL/J6 mice. Twenty-eight mice were used, seven per group. Specimens were stained with Giemsa dye. The osteoid tissue area was determined. Bone thickness was measured as an indicator of bone growth. Net bone growth was significantly increased in animals with zoledronic acid treatment: 0.02mm270.03mm2 in animals with particle implantation only (group 2), 0.25mm270.08mm2 with particle implantation and zoledronic acid treatment directly after surgery (group 3; p ¼ 0:0018), and 0.21mm270.11mm2 with particle implantation and zoledronic acid treatment on the fourth postoperative day (group 4; p ¼ 0:0042). The mean bone thickness was 0.2mm70.04mm (range 0.17 mm–0.31 mm) in group 1 (sham controls) and 0.16mm70.02mm (range 0.14 mm–0.19mm) in group 2, 0.31mm70.04mm (range 0.28 mm–0.39mm) in group 3, and 0.29mm70.02mm (range 0.28 mm–0.34mm) in group 4. Student’s t-test revealed a statistically significant difference between groups 2 and 3 (p ¼ 0:00042), and groups 2 and 4 (p ¼ 0:0019). In conclusion, our observational study suggests that zoledronic acid may stimulate bone apposition locally in the process of particle-induced osteolysis. r 2004 Elsevier Ltd. All rights reserved.