This sutdy evaluated whether differences in design of 3-dimensional pollactic acid barriers (Epi-Guide and Guidor) would influence hard tissue results in the treatment of Grade II furcations in humans. A multicenter study was conducted, using 40 patients with moderate to advanced bilateral chronic adult periodontitis of the mandibular first or second molars. After flap access, debridement, and root preparation, surgical bone level measurements were taken and membranes were placed on a random basis. Surgical reentry occurred at 1 year. Data collected from all 3 investigative centers were pooled and analyzed using an analysis of variance appropriate for a counterbalancing design. Both barrier materails resulted in significant gains of attachment level and defect reduction. The composite reduction in the vertical component of the osseous defects was greater in the sites terated with Epi-Guide as compared to those treated with Guidor; the difference between barriers reached statistical signficiance (P = 0.02)