The purpose of this study was to evaluate the sheep as a suitable animal model in which to compare periodontal wound healing after surgically induced Class II furcation defects were treated with different guided tissue regeneration (GTR) membranes. 22 mandibular second premolar sites in 11 sheep were used. The experimental design included untreated control teeth, sites treated by surgery alone, and others where surgery included placement of either Gore-Tex Periodontal Material (GTPM) or Gore-Tex Soft Tissue Patch (GTSTP). Sheep were killed 7 wk after surgery. Mesiodistal sections through decalcified second mandibular premolars were evaluated histologically. Histomorphometric analysis of digitized images allowed both area and linear measurements of newly regenerated furcal tissues. Percentage areas of cementum, bone, epithelium and connective tissue filling the furcation region were calculated. Coronal regeneration of alveolar bone and cementum were expressed as a percentage of the original height of the defect. Mean values for each group were subsequently analysed by 1-way ANOVA. Significantly greater regeneration was achieved with both of the GTR membranes, by comparison with the non-GTR surgical control group, with respect to percentage areas of cementum, bone and connective tissue, and the linear measurement of cementum (p < or = 0.05). This study demonstrates successfully the use of the sheep animal model for GTR research, and shows that few differences exist between GTR healing when either GTPM or GTSTP is used in the treatment of class II furcation defects.