Polylactic membranes were evaluated for vertical ridge augmentation around immediate implants in periodontally compromised extraction sites. Ligature-induced periodontitis was produced in 10 adult beagle dogs. The periodontium was allowed to heal for 6 weeks. All premolar teeth were extracted and three implants were placed immediately into the extraction sockets on either side of the mandible so that the polished cone extended above the alveolar bone level. On one side of the mandible, the implants were covered with a 0.2-mm-thick polylactic membrane (DL-lactide-co-trimethylene carbonate in a ratio of 7:3). Histologic and morphometric analyses performed after 3 and 5 months revealed that the membrane group did not exhibit significantly greater bone-implant contact that the controls. The occurrence of dehiscences correlated significantly with use of the membrane. Use of the membrane was associated with significantly less peri-implant bone height after 5 months. No remnants of the membrane material could be identified after 3 or 5 months, indicating rapid resorption during the first weeks of implantation. The tested membrane material did not fulfill the requirements of resorption kinetics and space maintenance for guided bone regeneration in vertical ridge augmentation.