Memory T-cells and activated B-cells were identified in cryostat sections of adult periodontitis (AP) lesions and categorized in terms of frequency and distribution. Nineteen periodontitis biopsies were obtained at the time of periodontal surgery to remove residual periodontal pockets following the completion of initial preparation. Gingival tissues exhibited various degree of inflammation (GI of 0-2) but probing depths of > 4 mm and > 5 mm loss of attachment. As a control, 5 gingivitis specimens (GI of 1, probing depth and loss of attachment of < or = 3 mm) were obtained from premolar and third molar sites requiring extraction for either orthodontic treatment or pericoronitis. Serial cryostat sections (6 microns in thickness) were prepared from each biopsy, on which a double staining avidin-biotin immunoperoxidase and avidin-biotin alkaline phosphatase technique was used to identify CD4+, CD45RO+ memory T-cells and activated CD19+ B-cells expressing CD23 or CD25. In periodontitis lesions, the mean percentage of CD4+ cells expressing CD45RO was consistently high (65.9% in the crevicular (C) one-third (1/3), 61.2% in the middle (M) 1/3 and 62.5% in the oral (O) 1/3). This contrasts with the low mean percentage of CD4+, CD45RA+ naive T-cells (17.1% in the C 1/3, 14.8% in the M 1/3 and 12.4% in the O 1/3). In gingivitis specimens, the incidence of CD4+, CD45RO+ was 81.9% in the C 1/3, 81.1% in the M 1/3 and 89.0% in the O 1/3. This was higher than that of periodontitis biopsies. With CD4+, CD45RA+ the incidence was 10.0% in the C 1/3, 8.0% in the M 1/3, and 6.6% in the O 1/3 and the relationship to the periodontitis biopsies was reversed. However, the percentage of CD23+ and CD25+, CD19+ B-cells which were identified in 13 out of 19 samples from periodontitis varied significantly (0-100% for CD23, 0-36.2% for CD25) in spite of similar clinical status. The frequency of B-cells and activated B-cells in the gingivitis was much lower than that of periodontitis. These results indicate that both T-cells and B-cells were in active stage in periodontitis lesions. Differences of immunohistological features between gingivitis and periodontitis may be attributable to the heterogeneity of profiles of cytokine production by CD4+, CD45RO+ "memory' cells.