Frozen gingival tissue sections from marginal gingivitis (MG), juvenile periodontitis (JP), adult periodontitis (AP) patients and clinical healthy subjects (H) were immunohistochemically stained with specific antibodies to aid in identification and quantification of different Ig bearing cells in inflammatory infiltrates. IgG, IgA, IgM, K and lambda were present in all specimens studied. The numbers of Ig cells in disease groups were much greater than in H group, especially the IgG cells. The numbers of IgG cells in AP and JP were most abundant, followed by MG and H. The correlation between the number of IgG cells and the percentage of infiltrated connective tissue was obtained by linear correlation analyses (r = 0.534, P < 0.001). This means that the inflammatory infiltration became heavier as the number of IgG cells increased. It is the new finding that the number of IgA cells was smaller than the IgM cells in JP, the IgA/total heavy chains ratio was much lower than other groups. The C3 deposition was found in all of the gingival specimens. In healthy gingival tissue, C3 mainly deposited in both of the surface of inflammatory cells and vessels. In diseased status C3 located not only in these two, but also in sulcular (pocket) epithelium and oral epithelium, Igs were also observed in these areas. It is suggested that immunocomplex may deposit in gingival tissue.