Flow cytometry was used to study the influence of smoking histories on autofluorescence, expression of surface markers, and phagocytic ability in alveolar macrophages (AM) recruited by bronchoalveolar lavage (BAL) from healthy smokers (n = 13) and nonsmokers (n = 13). Alveolar macrophages have an autofluorescence that can be quenched by a recently developed technique. In the present study, this technique was used in combination with flow cytofluorometry. Alveolar macrophages from smokers (mean 10.6 +/- 7.6 pack-years) showed a significantly (p less than .001) increased autofluorescence compared to nonsmokers. This autofluorescence was associated with an increased complexity of the cells but not with altered cell volumes. No correlation was seen between the mean fluorescence intensity and the cigarette consumption among smokers. Despite the difference in autofluorescence, no altered expression of surface markers known as markers of cell activation (HLA-DR, CR3) was detected in AMs from smokers compared to nonsmokers. The functional ability of AMs to ingest C3b-coated particles analyzed with a fluorescence quenching assay did not differ between the groups. The lack of correlation between the cigarette consumption and the autofluorescence suggests a maximal fluorescence intensity in the present population of smokers. The biological mechanism behind this autofluorescence needs to be further investigated.