A mineralogical analysis of lung tissue was conducted on 25 samples from patients who had been diagnosed as having idiopathic pulmonary fibrosis (IPF). Scanning electron microscopy (SEM) at low magnification and energy-dispersive x-ray analysis (EDXA) was used. In all samples, the surface silicon/sulfur (Si/S) ratio was calculated. The Si/S ratio for 25 samples of normal lung and 6 samples of pneumoconiotic lung was also determined (upper limit of normal Si/S ratio = 0.3). The difference between the Si/S ratio in the group with IPF and group with normal lung tissue was significantly significant (p less than .007, Wilcoxon test). Six of 12 patients with a previous diagnosis of IPF and a Si/S ratio greater than 0.3 had an exposure history that could imply inhalation of silica/silicates, and the correct diagnosis for these patients is most probably pneumoconiosis. The silica/silicate deposits detected in patients with IPF, and who had a ratio and no past exposure to dusts, could be either a cause or an effect of the disease.