We prospectively evaluated bronchial washings from 45 patients aged 1 month to 25 years (mean 3.3 years) for the presence of lipid-laden macrophages. By grading the amount of intracellular oil-red-O-positive material, we determined a semiquantitative lipid-laden macrophage index for each patient. All patients observed to be definite aspirators (n = 22) had indexes greater than or equal to 86 (mean +/- SD, 139 +/- 46). All patients with no clinical suspicion of aspiration (n = 23) had indexes less than or equal to 72 (mean +/- SD, 21 +/- 20). Our results suggest that simply sighting lipid-laden macrophages in a nonspecific finding, but quantitation of these cells may be a very good test for recurrent aspiration of food substances in children. This test appears to be more sensitive than radiographic studies.