PURPOSE: The purpose of this study is to evaluate the effect of exposure of hydroxyapatite coating on the amount of bone formation and stability in the dogs. METHODS: In this study, hydroxyapatite coated implants (HAPTITE) was placed over the femur bone surface of four dogs about 1 mm. The experimental group was divided into 4 weeks group of 8 implants and 8 weeks group of 8 implants, and then they were sacrificed. The stability of implants was evaluated twice with Osstell(TM) mentor (Osstell AB, Goteborg, Sweden) at right after placement and sacrifice. The amount of bone formation was evaluated through histomorphometric examination. RESULTS: The stability of implants was in normal range, and tended to increase as time goes by. Mean percentages of new bone formation rates were 90.5+/-6.6 at uppermost 1 mm bone level adjacent to soft tissues (level 1) and 92.9+/-4.1 at next 1 mm bone level (level 2) in 4 weeks group, 90.1+/-11.5 at level 1 and 95.9+/-2.3 at level 2 in 8 weeks group. Mean percentages of bone-implant contact rates were 85.1+/-10.8 at level 1 and 88.1+/-13.8 at level 2 in 4 weeks group, 88.5+/-14.4 at level 1 and 95.3+/-3.1 at level 2 in 8 weeks group. There was no statistically significant difference of new bone formation rate and bone-implant contact rate between uppermost 1 mm bone level adjacent to soft tissues and next 1 mm bone level. However, there was no significant difference in bone formation between 4 and 8 weeks groups. CONCLUSION: These results suggested that exposed hydroxyapatite coated implants to soft tissue showed favorable bone formation and implant stability.