Purpose: This study was undertaken to investigate the action of bisphosphonate on bone reactions after the placement of titanium screw implants into the tibiae of ovariectomized rats: Materials and Methods: Twelve-week-old female Wistar rats were divided into 4 groups of 18 animals each. The first group (Sham) was sham-operated, the second group (OVX) was ovariectomized only, the third group (Estrogen) was ovariectomized and received continuous estrogen with a 17beta-estradiol pellet, and the fourth group (YM-175) was ovariectomized and-received bisphosphonate at a dose of 10 mug/kg of body weight. Titanium screw implants were placed in the proximal metaphyses of. the tibiae 168 days after surgery. The animals were sacrificed 7, 14, and 56 days after implant placement. Undecalcified sections were prepared and evaluated by light microscopy. Histomorphometric measurements were obtained with a computer-based image analyzer to quantify the unit bone mass around the. implant and the rate of implant-bone contact. Results: Ovariectomies significantly reduced implant-bone contact and the bone volume around the implants. However, in the YM-175 group, only slight differences in both bone contact and bone volume were noted compared with the Sham and Estrogen group. The woven structure of new bone in the YM-175 group was also replaced by mature lamellar bone, as in the other groups. Discussion and Conclusion: These results suggested that bisphosphonate preserved the implant-bone contact and bone volume around the implants.