Bronchoalveolar lavage (BAL) was performed in 47 patients (24 smokers, 18 ex-smokers and 5 who never smoked). Cytocentrifuged preparations were stained with May-Grunwald-Giemsa (MGG) and differential counts of pulmonary alveolar macrophages (PAM) with smokers' inclusions were performed. The data supported an exponential reduction in this percentage and indicated that about 3 years elapsed before this percentage approximated to the values in patients who had never smoked. Electron microscopy was performed on eight BALs and the results supported those obtained by light microscopy.