This study describes (1) the composition of the "adhesive" type of periodontal membrane attachment onto resorptive surfaces of actively remodeling alveolar bone; (2) the structure of reversal lines in alveolar bone; and (3) the role of certain fibroblast-like "osteoclast companion cells" in the attachment process of periodontal fibers onto resorptive bone surfaces. Adesive attachments involve a layering of specific zones at the interface between the periodontal membrane and the resorptive bone surface, and one or more types of osteoclast companion cells appear to function in the secretion of components of proteoglycans (probably glycosaminoglycans) and precollagenous fibrils. The proteoglycans appear to serve as a principal component of the adhesive substance secreted on a bone surface and also as a binding agent for the linking and progressive relinking of new and old collagenous fibers to each other and to the resorbed bone surface. If a reversal in the direction of remodeling occurs, and new bone deposition occurs on a surface that was formerly resorptive, the zones of the adhesive interface become calcified and then constitute a "reversal line."