Guided tissue regeneration (GTR) using bioabsorbable barrier membranes has shown promising and somewhat predictable clinical results. However, limited information is available on the stages of histologic healing when these types of barriers are used. Therefore, the aim of this study was to compare three currently available bioabsorbable GTR barriers (type 1 collagen, polylactide/polyglycolide copolymer, and citric acid copolymer) for the treatment of surgically created periodontal dehiscences in dogs. Eight three-walled periodontal dehiscences were surgically created in the mandibles of six beagle dogs (four on each side of the jaw). The periodontal dehiscences were randomly assigned to receive one of the three barriers. One defect was left untreated to serve as a control. Histomorphometric analyses were conducted at 4 and 12 weeks. Data were analyzed using the Student-Fisher test. The membrane-treated group had a statistically significant increase in new bone formation and connective tissue attachment compared to the nontreated control sites. However, no statistical difference was noted among the various membranes. In addition, no difference was found between test and control sites when new cementum was examined. Sites treated with barrier membranes achieved greater bone regeneration than nontreated control sites in the canine model.