This study was designed to quantitate the changes in experimental angular bony defects and the surrounding tissues following the removal of irritants associated with marginal periodontitis. Plaque retentive ligatures were placed around the mandibular second bicuspids in each of four squirrel monkeys. Ten weeks later the ligatures were removed and mechanical cleaning was implemented. At the same time, ligatures were placed on the contralateral (control) bicuspids. After 10 weeks the monkeys were sacrificed and the tissues prepared for analysis. The control tissues represented the state of the periodontium immediately prior to ligature removal and the implementation of 10 weeks of mechanical cleaning. Histometric analyses revealed a reduction from 68 to 14% in the inflammatory cell infiltrate present in the supracrestal connective tissue following ligature removal and plaque control. Concomitant with this decrease was a 50% increase (P < 0.01) in the amount of bone present in the coronal periodontium. There was bone repair at the crest and along the angular defect but there was not a total regeneration of the lesion. These tissue changes were accompanied by a reduction in tooth mobility and a reformation of the gingival architecture although there was no new attachment. It appears that there is a potential for bone repair in these angular defects without an alteration in the connective tissue attachment level.