After the implantation of methylmethacrylate cement into the posterior part of the cervical spine of the dog, a thick layer of connective tissue forms at the bone-cement interface. The tissue is six to eight millimeters thick and in all animals it surrounds the dorsal and lateral aspects of the masses of implanted cement, grows between the undersurface of the cement and the bone of the posterior elements, and completely covers that bone. This tissue was examined by light and electron microscopy and its collagenous components were extracted and analyzed biochemically by gel electrophoresis. Specific extracellular matrix proteins in the tissue at the bone-cement interface were also localized by immunohistochemistry. The tissue at the host-cement interface contained zones of fibrocytes and plump and teardrop-shaped cells within a collagenous matrix. Type-I, Type-III, and Type-V collagen were extracted and were identified by gel electrophoresis. Type-V collagen and fibronectin were localized predominantly around the plump and teardrop-shaped cells. Type-IV collagen and laminin were localized predominantly in an area just beneath the teardrop-shaped cells at the surface of the tissue overlying the cement, suggesting that a basement-membrane-like tissue had formed in this area.