Autologous platelet concentrate (APC) contains concentrated platelet-derived growth factors that promote wound healing and tissue regeneration. The purpose of this prospective case series was to compare the treatment effects of an intralesional graft of APC to guided periodontal regeneration (GPR) using a bioabsorbable barrier membrane (MEM) over a 52-week period. Five patients were recruited for the study from two private periodontal practices. There were four females and one male having a mean age of 33 +/- 10.23 years. The five selected contralateral teeth had similar, but not identical, combinations of 1-, 2-, and 3-wall infrabony defects not involving furcations. Probing depths (PDs) of the defects were > or = 6 mm and had radiographic angular infrabony defects > or = 4 mm in depth. The patients had no local or systemic contraindications to minor oral surgical procedures and had not taken systemic antibiotics for > or = 6 months before the commencement of the study. All patients had completed cause-related periodontal therapy up to 6 months previously and had achieved a satisfactory level of oral hygiene. The selected teeth did not have purulent discharge from the pockets and responded normally to pulp sensibility testing. Patients were excluded if they smoked, were pregnant or lactating, or were allergic to any of the materials to be used in the treatment. At baseline and 8, 26, and 52 weeks after surgery, PDs, recession (REC), presence of plaque, and bleeding on probing were recorded, and standardized periapical radiographs were taken. At the time of surgery, the vertical distance to the deepest point of the infrabony defect was measured from the cemento-enamel junction (CEJ) to the buccal and lingual bone crests. The vertical distance to the base of the defect from the CEJ and defect angles were obtained from radiographs. The paired contralateral infrabony defects were treated with a graft APC or MEM after debridement and EDTA root surface conditioning. Surgical flaps were prepared and closed according to the papilla preservation method. Post-surgical care was provided at 1, 2, 8, 26, and 52 weeks after surgery. A mouthwash of 0.2% chlorhexidine gluconate was used twice daily for the first 3 weeks after surgery. Mean PD, REC, clinical attachment level (CAL), radiographic bone loss, and defect angle were computed and compared for each data collection point. From baseline to 52 weeks, a mean PD reduction of 3 +/- 1.41 mm (APC) and 3.6 +/- 1.67 mm (MEM), mean REC increase of 0.8 +/- 1.01 mm (APC) and 0.6 +/- 1.14 mm (MEM), mean CAL gain of 2.2 +/- 1.79 mm (APC) and 3 +/- 1 mm (MEM), mean radiographic bone fill of 3.24 +/- 2.85 mm (APC) and 2.7 +/- 1.9 mm (MEM), and mean defect-angle increase of 15.25 degrees +/- 18.21 degrees (APC) and 22.4 degrees +/- 27.3 degrees (MEM) were calculated. CAL gain was not related clearly to defect angle at baseline, although radiographic bone fill was slightly greater for defect angles <39.4 degrees +/- 7.88 degrees. This case series of five similar, but not identical, bilateral paired infrabony defects suggests that an APC graft achieves a similar CAL gain and PD reduction to GPR using an MEM over a 52-week period. A larger, controlled clinical trial is needed to evaluate further the efficacy of autologous platelet-rich plasma for the treatment of infrabony defects.