Objective: To compare the regenerative potential of bone graft used alone and in combination with barrier membrane in noncontained human periodontal infrabony defects. Method and Materials: Twelve patients (7 men and 5 women, 30 to 65 years of age) with moderate to severe chronic periodontitis were included in the study. A total of 16 one- or two-walled intraosseous defects were selected and randomly divided for decalcified freeze-dried bone allograft, alone (control group) or in combination with polylactic acid, polyglycolic acid barrier membrane (test group). Pocket probing depth (PPD), clinical attachment level (CAL), radiologic bone fill (RBF), and alveolar height reduction (AHR) were recorded immediately before surgery and after 3 and 6 months postoperatively. The ANOVA and Newman-Keuls post hoc tests were used for statistical analysis. A two-tailed probability value of P .05 was considered to be statistically significant. Results: For bone graft alone, PPD reduction was 2.00 ± 0.19 mm, CAL gain was 1.38 ± 0.18 mm, and RBF was 0.63 ± 0.26 mm: for the test group, PPD reduction was 2.75 ± 0.37 mm, CAL gain was 1.50 ± 0.27 mm, and RBF was 1.13 ± 0.23 mm. AHR for the control and test groups was 0.38 and 0.37 mm, respectively. Conclusion: These results confirmed nonsignificant clinical and radiologic differences in regenerative outcome with bone graft alone and with guided tissue regeneration in the treatment of noncontained human periodontal infrabony defects. Keywords: bone graft, combined periodontal regeneration technique, guided tissue regeneration, infrabony defect