The proliferating cell nuclear antigen (PCNA) is regarded as an operational marker of proliferating cells. We have used PC10 monoclonal antibody to PCNA to reveal proliferation sites in human dental pulp and gingiva. Intense PCNA-immunoreactivity was observed in the basal layer of the gingiva lining epithelium and within some cells of the underlying connective tissues, including some endothelial and perivascular cells. PCNA-reactive cells were scattered throughout the pulp tissue, but were particularly numerous in the peripheral part. Since PCNA is an endogenous cell cycle-related molecule, we propose that PCNA-antibodies may represent useful for studying cell kinetics in human oral tissues in normal as well as pathological situations, such as tumours, wound healing and inflammation.