In this study, clinical and histologic responses to a bioresorbable membrane used to obturate an osteotomy site in the lateral wall of the maxillary sinus and to facilitate graft containment were examined. Expanded polytetrafluoroethylene (e-PTFE) membranes were used as a cont rol to compare biocompatibility and resorption characteristics. Twelve sinus augmentation procedures were performed to facilitate placement of implants in nine patients with insufficient bone in the edentulous posterior maxillae. In five procedures, the lateral wall was obturated to ensure graft containment with an e-PTFE membr ane; the other seven were covered with a bioresorbable barrier (poly[lactic acid]). The presence or absence of inflammation, dehiscence, suppuration, and encleftation were recorded. All patients healed without complication or adverse biologic reaction to either barrier material. Biopsy specimens of the graft site were taken from the lateral wall with overlying soft tissue prior to reflection of the full-thickness flap at stage 2 surgery. Findings suggest that a poly(lactic acid) membrane can provide results similar to those with e-PTFE memb ranes for use in lateral obturation during sinus augmentation.