PREVIOUS INVESTIGATIONS have demonstrated that application of citric acid to a root surface results in exposure of dentin and/or cementum matrix collagen fibrils. Several studies have suggested a rapid and consistent connective tissue reattachment to citric acid treated roots. This study was initiated to determine if such an attachment was obtainable on human periodontally diseased teeth, in vivo, and could be confirmed through observations using the scanning electron and light microscopes. Full thickness flaps were raised on 18 single rooted teeth with moderate to advanced periodontitis. Citric acid (pH = 1.0) was applied to nine teeth with contralateral teeth serving as controls. Six to fifteen weeks later, the teeth with attached periodontal tissue were removed. Sagittal sections were obtained, with one-half of the root being processed for light microscopy and the remaining half studied by scanning electron microscopy. Six of nine citric acid treated roots provided evidence of fibrous attachment. Connective tissue was apposed directly to old or newly formed cementum, but never directly to dentin. Fibrous attachment was usually functionally oriented, i.e., perpendicular to the root surface. No evidence of fibrous attachment was found among the control specimens.