A female patient, healthy, non smoker, of 52 years olds, was referred to the periodontology department of I.U.E.M. to treat the bone defect on teeth 1.2, with probing pocket depth of 9 mm. A guided tissue regeneration was performed (GTR). The GTR is a surgical procedure that uses a barrier membrane, on an infra bony defect to maintain a blood clot in a space, to allow the periodontal attachment cell's to grow. The membranes of equine origin are three-dimensional estrutures of collagen, that have their effectiveness for 3 or 4 months, which is the necessary time for periodontal regeneration. The use of cortical-spongy bone substitute of equine origin, plays an important role in maintaining space, preventing the collapse of the membrane. The infra-bony defect had a probing pocket depth superior to 5 mm and a wide radiographic defect angle (superior to 37 degrees). In the presence of wide defects, the use of bone substitute is necessary. A modified papilla preservation technique was made and used a internal horizontal mattress suture. Follow-up appointments were made and standardized periapical radiographs were obtained through the use of an individualized device (paralleliser). Almost total bone filling was observed after 6 months and reduction of the pocket depth to 4 mm. The use of collagen membranes and corticocellular bone substitute of equine origin seems to be a viable alternative in the regeneration of infra-bony periodontal defects. Keywords: biomaterials of equine origin, infra bony defects, guided tissue regeneration, periodontal surgery