Collagen membranes were interposed between full thickness periodontal flaps and denuded root surfaces of right upper canines in 3 mongrel dogs; the left canines were sham-operated without the use of collagen membranes. Animals were killed 10 d after surgery. Tissue blocks were removed, and experimental and control sites were processed for histometric and histologic examination. The results indicate that collagen membranes: (i) prevent apical migration of the epithelium during initial stages of healing; and (ii) are colonized by connective tissue cells and incorporated within the healing connective tissue.