A study was conducted to determine the ability of demineralized bone matrix gel to act as an osteoconductive/osteoinductive materiaI to enhance cenine spinal fusion. Seven dogs underwent posterior spinal fusion, Four-level fusions were performed with one of four procedures at each level: decortication alone, with gel added, with autograft, or with both gal and autograft. Dogs were killed at 6 weeks ano early histologic response was studied. At untreated control sites, little bone formation was evident. Gel-filled sitas showed abundant osteoid, with 60% of deminerallized particles fused to or surrounded by new bone. Sites filled with autograft had more new bone, but there was more osteoid at gal-treated sites. Autograft augmented with gel showed the most vigorous response with extensive bridging between demineralized particles, host bone, autograft, and new bone. Significantly less autograft was needed to induce a similar amount of now bone formation when gel was added. Use of the gal as an autograft extender may improve the chance for successful spinal fusion.