Specially prepared biphasic calcium phosphate (BCP) macroporous ceramics consisting of an intimate association of beta tricalcium phosphate (P-TCP) and hydroxyapatite (HA) with P-TCP/HA weight ratios of 15/85, 35/65, and 85/15 were implanted in surgically created periodontal osseous defects in dogs and recovered after 6 months. A decrease in average size of crystals in BCP ceramics and an increase in the size of microporosities in the surface and at the core of the ceramic after implantation were observed, indicating that in ziivo dissolution has taken place. The resorbability (reflecting in vivo dissolution) of BCP ceramics depended on their P-TCPIHA ratios, the higher the ratio, the greater the resorbability. The formation of microcrystals with crystallographic properties and Ca/P ratio similar to those of bone apatite crystals were also observed. The abundance of these crystals were directly related to the P-TCP/HA ratio of the BCP ceramic before implantation. The formation of the bone apatite-like crystals may be due to the precipitation of calcium and phosphate ions released from the dissolving ceramic crystals (the P-TCP component dissolving preferentially to the HA component). Results from this study suggested that one of the means of controlling resorbability (in uivo dissolution) of BCP ceramic is by varying its P-TCP/HA ratio. surgery.'-'' In vitvo P-TCP ceramic showed greater extent of dissolution in *Request for reprints and other correspondence. This article was resented in part at the Third World Biomaterials Congress, Kyoto,