The purpose of this controlled clinical trial was to compare the efficacy of two surgical approaches to protect the regenerated tissue following membrane removal in guided tissue regeneration (GTR) treated intrabony defects. Twenty-eight (28) defects, one each in 28 patients were randomly assigned after placement of the membrane to one of two treatment groups by blocking to prognostic variables. The test group received free gingival grafts on the interproximal regenerated tissue. In the control group the surgical flaps were coronally positioned over the regenerated tissue. The two groups were well balanced with respect to all prognostic variables. The results indicated that: 1) similar amounts of regenerated tissue were obtained in the two groups at membrane removal (7.6 +/- 2.8 mm, test; 8.3 +/- 2.3 mm, control); 2) a significantly greater amount of probing attachment level gain was observed in the test group (5.0 +/- 2.1 mm, test; 3.7 +/- 2.1 mm, control). This study indicated that placement of free gingival grafts on the interdental regenerated tissue further improves the clinical outcome of GTR in deep intrabony defects.