The precise factors mediating both initial cell attachment and longer term connective tissue reattachment after tissue destruction due to periodontal disease are not known. An in vitro model was used to assess initial attachment of fibroblast-like cells to periodontally-diseased root surfaces. Root fragments were obtained from freshly extracted teeth from 6 different patients. Individual roots were prepared such that a comparison could be made of initial attachment to non-instrumented diseased root surface, curetted diseased root surface and the non-diseased, non-instrumented portion of the same root. The amount of hard tissue removed by instrumentation was quantitated and kept constant between 0.9-1.0 mm. The unsterilized fragments were incubated with human gingival fibroblasts (HGF) for 1 h at 37 degrees, after which the roots were first washed to remove non-adherent cells and then photographed. The number of attached cells per unit area was quantitated from the photographs using a grid system. No significant differences could be detected between the numbers of cells attached to the 3 types of root surfaces studied on the individual roots or between any of the roots studied. Thus, initial attachment of HGF to diseased root surfaces is not inhibited by the presence of plaque or endotoxins.