The purpose of this study was to compare the effectiveness of polylactic acid (PLA) granules as an alloplastic grafting material to that of decalcified freeze-dried bone allograft (DFDBA) and a flap procedure for debridement without graft (FPD) when treating periodontal intrabony defects. Ten patients presenting with advanced adult periodontitis, including at least 3 similar periodontal osseous defects (2- and 3-walled), comprised the study group. After completion of a hygienic phase of treatment, measurements were made with calibrated periodontal probes and stents to determine soft tissue recession, probing pocket depths, and probing attachment levels. Each defect was surgically exposed and hard tissue measurements were obtained. Defects were treated with one of the 3 methods above chosen randomly prior to the surgical appointment. Six months postsurgery, soft tissue measurements were repeated and all sites were surgically reentered to obtain hard tissue measurements. All surgical sites healed without clinical complication. The initial pocket depths and initial depth of osseous defects were compared between the groups using ANOVA and no significant differences were found. A mean osseous defect fill of 0.4 mm (11.2%) occurred with the flap procedure for debridement, 3.0 mm (65%) with DFDBA, and 0.1 mm (2.2%) with PLA. Mean crestal bone loss was 1.30 mm for FPD, 0.60 mm for DFDBA, and 1.55 mm for PLA. No statistically significant differences were found in soft tissue recession between groups or in the osseous defect measurement between PLA and FPD. A statistically significant improvement (P < 0.001) was found in the fill of the osseous defects when using DFDBA compared to the initial defect depth and to the other 2 groups.(ABSTRACT TRUNCATED AT 250 WORDS)