The purpose of this study was to compare the phenotypic distribution of resident gingival mononuclear inflammatory cells from tissues associated with peri-implantitis and periodontitis. Inflamed gingiva was obtained from six patients during surgical removal of failed dental implants. Similarly, inflamed gingiva around teeth was obtained from eight patients with moderate to advanced periodontitis. Monoclonal antibodies were used to identify membrane antigens from CD4+ T-lymphocytes, CD4+/CD8(+)-activated T-lymphocytes, tissue macrophages, CD20+ B-lymphocytes, and MHC class II (Ia) antigens. Gingival inflammation associated with both dental implants and natural teeth was characterized by substantial numbers of CD4+ T-lymphocytes, resident macrophages, and B-lymphocytes. In addition, there was an abundance of HLA class II-positive mononuclear cells throughout most specimens. These results suggest that the gingival mononuclear inflammatory response in peri-implantitis and periodontitis is similar and support the hypothesis that similar inflammatory mechanisms are associated with both conditions.