Bronchoalveolar lavage, performed on 15 healthy volunteers, enabled quantification and characterization of the alveolar cell populations. The subjects studied were 8 nonsmokers (5 males, 3 females) and 7 smokers (6 males, 1 female). It was found that in the smokers the macrophages increased compared with nonsmokers, both in absolute number (419,000 vs. 138,000/ml; p less than 0.005) and in percentage (93.8 +/- 3.0 vs. 88.1 +/- 4.8%; p less than 0.02), causing a significant increase in the total number of cells recovered after bronchoalveolar lavage (471,000 vs. 163,000/ml; p less than 0.005). Lymphocytes and neutrophils do not significantly vary in the two groups, even though among the smokers there is a tendency for the concentration of these cells to increase in the lavage liquids. The importance of the data obtained from healthy subjects lies in the possibility thus afforded of having reference values for the study of various lung pathologies with bronchoalveolar lavage.