This study compared the effect of diameter and length on the pullout force required to extract hydroxylapatite-coated implants from dog alveolar bone. After 15 weeks for integration, implants of 3.0, 3.3, and 4.0 mm diameter and 4, 8, and 15 mm length were pulled. The results showed that the ultimate pullout force correlated strongly to implant length, but not diameter. Cortical bone contributed more to implant retention than cancellous bone.