The distribution and the density of gamma delta T cells in human gingival tissues were examined immunohistochemically in biopsy samples obtained from 20 subjects. Few gamma delta T cells were observed in gingival tissue free from inflammatory cell infiltration, but were found, albeit in low numbers, in association with inflammatory cell infiltration, especially T cells. This relationship with T cells was confirmed statistically. The ratios of gamma delta T cells to T cells in the epithelia and in the connective tissue were calculated in the sections in which more than 500 CD3-positive cells were identified. Seven of eight such epithelial specimens showed a ratio of less than 1% and one less than 2% (mean +/- SD; 0.8% +/- 0.4). In the connective tissue, 8 of 13 such specimens showed less than 1%, three less than 2%, one 3%, and one 7% (1.4% +/- 1.9). These results suggest that basically gamma delta T cells are not resident cells in the gingival epithelium such as comprise the first defense line against exogenous irritation. They may play some role in the pathogenesis of periodontal disease collaborating with alpha beta T cells in the inflammatory response.