Cyst-like cavities in the jaw bone often heal incompletely owing to ingrowth of connective tissue, thus preventing osteogenesis from occurring. In the present study, a new membrane technique has been utilized in an attempt to improve bone healing. By means of an inert, porous membrane, placed in close contact with the bone surface, a secluded space is created which can only be repopulated by cells from the adjacent bone. Thus, osteogenesis is able to occur without interference from other tissue types. Through-and-through bone defects were produced bilaterally (1) in edentulous areas of monkey (n = 5) mandibles, and (2) in conjunction with apicectomy of the lateral maxillary incisors, also in monkeys (n = 7). On one side, the defects were covered buccally as well as lingually/palatally with expanded PTFE membranes, whereas the defects on the other side served as controls (no membrane). In the mandible, complete bone healing was seen at all test sites after a healing period of 3 months. On the control side, 3 experimental sites showed bone discontinuity with a transosseous core of connective tissue, whereas some bone healing had occurred lingually at 2 sites, but with massive soft tissue ingrowth from the buccal side. In the maxillary periapical defects, all the membrane-covered defects had healed with bone closure after 3 months but with a minute portion of connective tissue, probably derived from the periodontal ligament, around the tooth apices. None of the control defects (no membrane) healed spontaneously, but all were filled with connective tissue to varying degrees.(ABSTRACT TRUNCATED AT 250 WORDS)