Cell surface phenotypes of bronchoalveolar lavage (BAL) and peripheral blood lymphocytes (PBL) obtained from a group of young healthy volunteers, including smokers and nonsmokers were studied. Results indicate that the proportions of T (CD3+) and B (CD19+) lymphocytes were comparable in PBL and BAL lymphocytes, whereas the numbers of cells bearing natural killer cell-associated markers (CD16, CD11b, CD56, and CD57) were significantly higher in PBL; in BAL lymphocytes of smokers, the CD4+/CD8+ ratio was < 1. The surface density of CD3 in every case was lower in BAL T cells. The expression of different surface antigens considered to reflect lymphocyte activation was variable; the human lymphocyte antigen (HLA)-DR, CD25 (alpha chain of the interleukin-2 receptor), and CD71 (transferrin receptor) were displayed at low levels in both types of samples. In contrast, the expression of 4F2, CD49a, and particularly, the early activation antigen CD69 were significantly higher in BAL cells compared with PBL; BAL samples from smokers included significantly lower proportions of lymphocytes bearing the CD69, HLA-DR, and 4F2 activation antigens.