Objective: The aim of the present study was to compare the efficacy of guided tissue regeneration (GTR) using 2 different biodegradable barriers (polylactide acetyltributyl citrate; polydioxanon) in 3- and 2-wall infrabony defects. The polydioxanon barrier is an experimental membrane for GTR therapy that consists of a continuous occlusive barrier that has a layer of slings on the side that is meant to face the mucoperiosteal flap. Material and methods: 15 patients provided 15 pairs of similar contralateral periodontal defects: 12 predominantly 2-wall and 18 predominantly 3-wall infrabony defects. Each defect was randomly assigned to treatment with either polylactide acetyltributyl citrate (control [c]) or polydioxanon (test [t]) devices. At baseline, 6, 12, 18 and 24 months after surgery, clinical measurements (PlI, GI, PPD, PAL-V) were performed and standardized radiographs obtained (not at 18 months). Results: Both treatments revealed a significant GI reduction (p 0.05). A statistically significant gain of bone within the infrabony pockets was measured for both treatment options 24 months postsurgically [2.89±2.51 mm (t), 2.14±2.63 mm (c); p Schlagwörter: biologisch abbaubare Barrieren, approximale infraalveoläre Defekte, röntgenologischer Knochengewinn