To evaluate the efficacy of guided tissue regeneration around exposed implant threads, 16 implants were placed into fresh extraction sockets in beagle dogs. Polytetrafluoroethylene (e-PTFE) membranes and titanium membranes were used to cover the defects around implants. A control group did not receive any membranes. Results were evaluated histologically. The average gain in bone height was 2.1 mm for e-PTFE sites, 0.8 mm for titanium membranes, and 2.9 mm for control sites. The greatest gain in bone levels was seen for two sites that received e-PTFE membranes and remained covered for the entire evaluation interval. Within the limits of this study, clinical and histologic evidence demonstrated that, when primary coverage is maintained, the use of e-PTFE membranes can significantly enhance bone regeneration around implants.