Biphasic calcium phosphate, consisting of B-tricalcium phosphate and hydroxyapatite, was implanted in wide and deep periodontal osseous defects of monkeys in combinatoin with the guided tissue regeneration technique. After 12 weeks, sites treated with a combination of biphasic calcium phosphate and guided tissue regeneration maintained the shape of the ridgem but both guided tissue regeneration and control sites (untreated) showed extreme resorption. A histopathologic investigation revealed that numerous machrophages contained small particles of ceramic within their vesicles and that active bone replacement occurred from the surrounding bone. Biphasic calcium phosphate has osteoconductive potential and this potential may be related to degradation by macrophage phagocytosis.