Alveolar macrophage function was studied immunocytochemically using three monoclonal antibodies--macrophage CD 68 KP 1 (M), protein CD 11C (P), and anti-elastin (EL)--and three polyclonal antibodies--lysozyme (LZ), alpha-1-antitrypsin (AAT), and alpha-1-antichymotrypsin (AACT). The material for study was smears obtained from bronchial washings from 15 healthy persons and 60 patients with respiratory infections or primary or secondary malignant lung infiltration. Eight of the healthy group and 40 of the patient group were smokers (SM). The percentage of cells obtained from the washings which were macrophages was also measured. The intensity of staining reactions for each of the six antigens was noted and in general more intense staining was noted in smokers than in non-smokers. More intense staining was observed in patients with pulmonary infections (group II PI) and metastatic pulmonary infiltrations (group IV MP Ca) than in controls (group IC), while patients with primary lung cancer (group III PP Ca) had highly reduced staining reactions. The number of macrophages was similarly increased in all groups in comparison with the IC group for non-smokers and in all groups except III PP Ca for smokers. It is concluded that smoking, pulmonary infections, and metastatic infiltration of the lung are associated with an increase in the number and activity of alveolar macrophages, while patients with primary lung cancer have an increase in the number of macrophages which are functionally incompetent.