Created periodontal defects in dogs were randomly assigned for experimental (Guidor bioresorbable membranes) or control (conventional therapy) treatment. The results showed t hat the new connective tissue attachment was significantly greater in test sites than in controls. This new attachment averaged 2.79 ± 0.74 mm and 1.47 ± 0.20 mm at test and control sites, respectively (P 0.05). Epithelial downgrowth was also reduced in the test sites (P 0.05). No differences in bone response were found. The bioresorbable barrier was effective in blocking gingival epithelial downgrowth and connective tissue proliferation, promoting new attachment according to the principles of guided tissue regeneration.