Four consecutive chronic, severe periodontal bone defects in anterior teeth were treated by guided tissue regeneration, using a polytetrafluoroethylene periodontal membrane. The root surface was not specifically conditioned, and osseous grafts were not used. However the membrane was manipulated so that space under it was maintained. This was accomplished by painting the outer surface of the membrane with butyl-cyanoacrylate, so that it became rigid. The membranes were removed after 4 weeks and a bone-like tissue was found in all cases. The clinical results suggest that there was a relationship between the amount and quality of the new tissue and the volumetric characteristics of the available space.