This study clinically evaluated a bioabsorbable barrier membrane designed for periodontal regeneration. Ten Class II furcations and 12 interproximal infrabony defects were treated by flap debridement and placement of a bioabsorbable barrier membrane using the principles of guided tissue regeneration. Treatment was evaluated in terms of changes in vertical probing depth, horizontal attachment level, clinical attachment level, and recession. Baseline data were collected on the day of surgery, and outcome measurements were performed at the 1-year appointment. The mean initial probing depth for Class II furcations was 6.5 mm. At 1 year, the mean probing depth was reduced to 2.9 mm, a 3.6 mm change. These differences were clinically and statistically significant (P < 0.01). There was a mean gain of 2.4 mm in clinical attachment level (P < 0.01) and a mean 3.4-mm change in horizontal attachment level (P < 0.01). Recession increased 1.2 mm. For interproximal infrabony defects, there was a mean probing depth reduction of 5.0 mm (P < 0.01), a mean gain of clinical attachment level of 3.8 mm (P < 0.02), and a mean increase of 1.2 mm in recession (P < 0.04). The results indicate that significant improvements occurred after treatment of Class II furcations and interproximal infrabony defects with the use of a bioabsorbable barrier membrane and guided tissue regeneration.