The purpose of this investigation was to evaluate, in humans, the use of Kielbone as a substitute for fresh autogenous bone in treating periodontal intrabony defects. A total of 92 intrabony defects were treated with a previously described new attachment procedure utilizing free mucosal grafts to cover the intrabony defects following bone grafting. Kielbone was placed in 46 of these defects, while the remaining 46 defects were treated with autogenous bone grafts. The results were evaluated after 6 months by periodontal probing and assessment of the bone level as seen on periodical, identical radiographs. No differences were observed between the amount of clinical gain of attachment obtained in defects treated with Kielbone and those treated with autogenous jaw bone. This indicates that in surgical procedures attempting to restore lost connective tissue attachment, Kielbone constitutes a suitable replacement for fresh autogenous bone. The results are discussed in th light of recent studies that challenge the beneficial effect of bone grafts in the treatment of intrabony defects.