To investigate the effect of chronic smoke exposure on pulmonary macrophages (PM), the expression of seven different surface and intracellular molecules of PM was studied in induced sputum (IS) samples from healthy volunteers--nine smokers and seven non-smokers. Sputum was induced by inhalation of nebulized saline (3.5% NaCl). Cell viability and total cell counts (TCC) were performed immediately. Cell differentials were determined on May-Grunwald Giemsa-stained cytospin preparations. The PM were immunologically characterized by use of the following monoclonal antibodies: RFD1, RFD7, CD11b, CD54, CD68, CD71 and HLA-DR. The stainings were performed with a three-step, indirect immuno-alkaline phosphate method. Viability and TCC did not differ between the groups. Smokers had a higher percentage of macrophages (P < 0.05) and a lower proportion of neutrophils (P < 0.05). The percentage of macrophages expressing RFD1, HLA-DR, CD71 (P < 0.01 for all) and CD54 (P < 0.05) was significantly lower in smokers, whereas the remaining markers were expressed equally in the two groups. The results indicate that smoking induces a decrease in the expression by PM of surface molecules known to be associated with the antigen-presenting function.