The lymphocyte populations and subpopulations extracted from inflamed periodontal tissues of patients with adult periodontitis were determined. 34 patients were grouped according to the gingival index score (GI) of 1, 2 and 3. Gingival tissue from 2 involved teeth was excised, treated with collagenase, and infiltrating cells were isolated and identified using monoclonal antibodies for lymphocyte sets and subsets. The % of CD3+ cells was about 54.5% in all 3 patient groups, but the percentage of CD22+ cells increased from 28.9 +/- 3.3% in the group with GI = 1 to 33 +/- 1.2% in the group with GI = 3. %s of CD4+ cells and activated CD4+ cells increased from 30.2 +/- 2.1% and 4.7 +/- 1.7% in the group with GI = 1 to 38.4 +/- 1.2% and 16.0 +/- 3.4% in the group with GI = 3, respectively, while in the same groups, the % of CD8+ cells decreased from 24.9 +/- 2.0% to 17.7 +/- 1.6%. These data indicate a possible importance of activated CD4+ cells in pathogenetic mechanisms of periodontitis.