Normal gingival tissues of BNL mice of different ages were studied, using recently developed immunohistochemical techniques to detect T and B lymphocytes, Langerhans cells and macrophages. The presence of mast cells, plasma cells and neutrophils was also determined. Cell densities were determined in the epithelium and connective tissue compartments of the attachment area, the papilla and the diastema. T lymphocytes (Lyt 1*) were present in the epithelium and connective tissue of all three areas studied. Their numbers increased significantly with age in the attachment area and in the papillary connective tissue. Langerhans cells (F4/80*) were detected in the epithelium of all three areas examined. Their numbers did not vary significantly with age. The highest concentrations of T lymphocytes and Langerhans cells were observed in the attachment area at all ages. Macrophages (F4/80*) were detected in the connective tissue of all three areas examined. Their numbers increased significantly in the papillary connective tissue of older animals (78 weeks of age). Neither B lymphocytes (RA‐2C2′) nor plasma cells were detected in any of the tissue areas examined. The presence of neutrophils in the attachment area increased with age. Mast cells were present in all samples in the more vascularized areas (the papilla and diastema). The results suggest that, throughout the lifespan, T lymphocytes, macrophages, Langerhans cells and mast cells are normal constituents of the oral mucosa of the mouse, while B lymphocytes, plasma cells and, for the most part, neutrophils are absent under normal conditions. Furthermore, the concentrations of T lymphocytes and macrophages increased with age in the areas adjacent to the dentition, possibly as a result of reduced tissue resistance to external antig