Lymphocyte infiltration of central airway epithelium was evaluated in 13 normal nonsmoking subjects (Group 1), in 11 smokers without clinical signs of chronic bronchitis (Group 2), and in 34 patients who were smokers with chronic bronchitis and mild airflow limitation (Group 3). Bronchial samples were obtained through fiberoptic bronchoscopy. Murine monoclonal antibodies directed against cell-surface antigens and an immunoperoxidase technique were used on cryostat sections to label in situ the following lymphocyte populations: T-lymphocytes (CD3+), helper/inducer T-cells (CD4+), suppressor/cytotoxic T-cells (CD8+) and B-lymphocytes (leu 12+). Virtually no B-cells were found in central airway epithelium from subjects of any group. Conversely, consistent infiltration of epithelial layers with T-lymphocytes of both subsets was observed in all subjects, with a constant predominance of CD8+ over CD4+ cells. For any T-cell marker, differences between mean scores from Group 1 and Group 2 subjects were not statistically significant. On the other hand, mean lymphocyte numbers of both subsets were found increased in patients from Group 3 compared with subjects from the two other groups: statistically significant differences were observed for CD3+, CD4+, and CD8+ cells (p less than 0.001). Furthermore, lymphocyte scores at two different airway generation were compared in some patients from Groups 2 and 3, and a significant positive correlation was observed. These results suggest that T-lymphocyte infiltration of central airway epithelium (1) may be a naturally occurring phenomenon that is amplified in the airways of smokers with chronic bronchitis, and (2) may represent the counterpart to the intraepithelial population of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)