Periodontal healing after use of Atrisorb barrier material (polylactic acid) for guided tissue regeneration was studied in the premolar and molar teeth of six beagle dogs. Defects studied were surgically induced or were caused by naturally occurring periodontitis. Barriers fragmented and became displaced in 2 to 5 weeks after application. Granulation tissue was sometimes present between the barrier and root surface at 10 days to 4 weeks. Several sites were surgically reentered at 4 months, and new bone covered 60% to 100% of the formerly exposed furcations and root surfaces. Sites obtained for histologic evaluation 9 to 12 months after the baseline surgery showed new connective tissue attachment, cementum, and alveolar bone. Histomorphometric analyses quantitated these tissue changes, and new connective tissue attachment covered 72% of surgically exposed root surfaces and 77% of periodontitis-exposed root surfaces. It was concluded that new periodontal supporting tissues became reconstituted on root and furcation surfaces after use of the Atrisorb barrier material for GTR.