The dynamics of bone turnover in the furcations of teeth treated with expanded polytetrafluoroethylene (ePTFE) membranes were evaluated using multiple fluorochrome labels in 6 male beagle dogs. Loss of attachment involving the furcation area was induced in the second, third, and fourth premolar teeth using silk ligatures. The resulting defects were treated with the use of mucoperiosteal flaps for access, debridement of the defects, and placement of ePTFE membranes covering the furcations of the second and fourth premolars (experimental teeth) while the third premolar received only debridement without membrane placement (control tooth). Five fluorochrome labels were administered intravenously at timed intervals to act as markers of the osseous response. Membranes were removed at 4 weeks and all animals were terminated at 12 weeks post-membrane placement. One side of the mandible was decalcified, sectioned at 7 microns, and stained with either hematoxylin and eosin or Gomori's tri-chrome. The opposite side provided non-decalcified tissue processed as 100 microns ground sections. Using fluorescent light and point-hit evaluation, tissue in the coronal half of each specimen was classified as either labelled bone, unlabelled bone, or resorption space. In addition, microradiographs were prepared of each ground section and specimens classified as either woven bone, old lamellar bone, or new lamellar bone. No significant differences in attachment levels, or level of junctional epithelium, were observed in decalcified sections although greater remodeling activity was noted in the experimental specimens. Comparison of ground sections revealed significant differences (P < 0.05) in all categories with both methods of evaluation.(ABSTRACT TRUNCATED AT 250 WORDS)