Three different membranes were tested for guided bone regeneration in 8‐mm unicortical trephine defects in rabbit tibia. All experimental and control defects healed with bone. The critical size defect in rabbit tibia is larger than 8 mm, because control defects, 8 mm in diameter, healed spontaneously. Around remnants of the biodegradable Polyglactin 9 10 mesh (Vicryl®). a diffuse infiltration of inflammatory cells with multinuclear giant cells developed. However, the bone healing was not impaired by the infiltrate. Around the Gore‐Tex® membrane and around remnants of the Alzamer® a few lymphocytes were observed, but no multinuclear giant 1 cells were noted.