This study comprised 30 patients who had not been exposed occupationally to dusts, but for whom a diagnosis of suspected pulmonary carcinoma had been made. Bronchoalveolar lavage fluids from these patients were analyzed by transmission electron microscopy and by energy-dispersive x-ray microanalysis in an effort to study the mineral particulate present in the alveolar region. Particles of silica, silicates, oxides, sulphates, and metal alloys were detected in various percentages in each subject. The smoking habits of two groups of patients that were defined by their bronchoalveolar lavage particulate concentrations (i.e., lower or higher than the median of the distribution) differed significantly.