Platelet degranulation can resultin the release of a variety of factors which are chemotactic, mitogenic, and angiogenic, making platelets extremely important in the regulation of the repair process. This study examines how various types of root surfaces affect platelet deposition and the release of serotonin from dense granules. In addition, experiments were performed to evaluate the effects of the cyclo‐oxygenase inhibitor, indomethacin, on platelet deposition and dense granule release. Roots from freshly extracted teeth from sites with periodontal disease (PD) and from healthy sites were sectioned and had the following surface conditions: 1) periodontal ligament present; 2) PD; 3) PD, root planed; 4) PD, root planed and demineralized; and 5) condition 4 treated with collagenase. In addition, rabbit calcaneal tendon collagen was used. All samples were incubated with platelets labeled with both111Indium and14C serotonin, with and without the addition of indomethacin. It was observed that the greatest number of platelets deposited on the tendon collagen. Furthermore, serotonin release occurred on all samples except PD and indomethacin partially inhibited platelet deposition on all samples except tendon collagen. Finally, indomethacin inhibited serotonin release on all surfaces. These results suggest that attachment of platelets to the root surface is facilitated by metabolism through the cyclo‐oxygenase pathway and that limited platelet deposition can occur in the absence of dense body release.J Periodontol 1992; 63:33–38.