The aim of the present study was to evaluate periodontal tissue alterations during the maintenance phase following GTR therapy. 18 patients (average age 54 years, range 39-79 years) with 19 local periodontal defects were monitored longitudinally using clinical periodontal parameters and radiographic assessments of bone level changes. 6 out of originally 24 patients were not available at the 4-year examination (2 patients were unwilling to participate and in 4 patients root amputations or tooth extractions had to be performed). Evaluations were performed at baseline, 3 months, 1 year and 4 years following GTR therapy (using non-resorbable Gore-Tex Periodontal Material). The changes observed at the deepest site of each tooth treated by GTR were compared to those encountered in the entire dentition. Supportive periodontal therapy was performed according to the patient's individual needs between 3 and 12 times between the 1 and 4 years examination. The plaque index and the gingival index at the 4 years examination were assessed and had increased to almost double the value of baseline, although the BOP remained lower compared to baseline data. Between the 1 and 4 years examinations, 1.27 mm of clinical attachment was lost as a mean. Regarding the site of each tooth treated with GTR with the initially deepest probing pocket depth, 1.42 mm of clinical attachment was lost during the maintenance phase. However, compared to baseline data, 1.37 mm of new attachment could be maintained. The clinical attachment level was maintained within +/- 1 mm in 12 out of 19 sites during the 4 years of maintenance.(ABSTRACT TRUNCATED AT 250 WORDS)