After periods of observation from 3 to 36 months, biopsies were obtained from 22 patients in whom porous block and particulate hydroxylapatite ceramic (Interpore 200™)) had been used for augmentation procedures and in two patients in whom nonporous particulate hydroxylapatite (Calcitite ) had been used. Histologic examination of serial sections of decalcified specimens revealed vital bone formation in relation to the blocks, whereas the particulate was encapsulated in fibrous tissue. The differences in biological behavior are discussed. Keywords: biopsy, bone ingrowth, histology hydroxylapatite, porous ceramic, ridge augmentation