Extensive epidural scar formation is a well-known complication after spine surgery. Fibrous adhesions around nerve roots are a major reason for recurrent neurological symptoms following lumbar discectomy. A large variety of materials, implanted onto the dura, have been used to prevent or reduce laminectomy membrane, with conflicting results. We therefore carried out an experimental study in dogs to compare those materials that seemed to be most suitable. In each of 30 adult beagles, three lumbar laminectomies were performed. Each level was covered with a different material--free autologous fat graft, cellulose mesh, Gelfoam or triamcinolone suspension. In a control group nothing was implanted. After 7 days or 1, 3 or 6 months the animals were killed. The lumbar vertebral columns were harvested and prepared for further histological examination. To compare the results, we designed a new classification scheme (scar index). The data were obtained without knowledge of implanted material or time since operation. We found that free autologous fat grafts are able to reduce epidural scar formation in a high proportion of cases, especially after 3 and 6 months; cellulose mesh showed the worst results. We conclude that free autologous fat grafts are superior to other materials because of simple operative handling, good compatibility and effective prevention of laminectomy membrane.