Nowadays, different materials have been used for regeneration of interosseous defects and Neo-Os is one of them. The objective of this study was to evaluate histologically the influence of Neo-Os® particles on bone regeneration using rabbit caivarias defects with and without protection of Gore-Tex® barrier membrane. A cutaneous- periosteal incision and flap was made on the forehead of 32 rabbits exposing the top o"" the skull. A standardized trans-osseous skull defect (8 mm diameter) was made in each of the parietal bone with rotating round bur. In half of the rabbits, one defect was filled with the Neo-Os® particles without any type of the barrier membrane. The other defect was left empty. In the other half of the rabbits, one defect was filled with Neo-Os® and two flat expanded polytetrafiuoroethyiene (Gore-tex®) membranes. For the other defect, only the Gore-tex membrane protected the defect. After 8 and 16 weeks, the specimens were processed using standard, decalcified, hard tissue histology techniques. Rabbit caivarias defects treated with Neo-Os® particles and polytetrafiuoroethyiene (Gore-tex®) membrane, healed by in growth of woven bone from the defect margins and by formation of bony islands within the defect area. Finally, the defects were treated with woven and lamellar bone.