The data from analysis of the particle contents of human lungs, without overt pneumoconiosis, were summarized. This update included analysis of a total of 75 lungs. Previous reports have included analysis of 33, 35, and 48 lungs. Lungs were obtained from cadavers of urban residents from the Cincinnati area, with an age range of 23 to 96 years and a median age of 66 years, all of whom died of natural causes. There were approximately equal numbers of males and females, and blacks and whites. Fifty five of the subjects were smokers, and 37 were nonsmokers. Occupations of the subjects included: foundry workers, machinists, farmers, salesmen, domestics, clerical workers, and homemakers. Scanning electron microscopy and energy dispersive x-ray analysis were employed in the analysis of the particle contents of the lungs. The mean exogenous particle concentration was 613 +/- 601 million particles per gram of dry lung. The particle contents of the lungs were very similar. The most frequently found species in 60 of the 75 lungs were aluminum silicates. Other commonly found particle types included silica, iron-oxides, rutile, and magnesium silicates, which together with aluminum silicates made up 75 percent of the exogenous particle burden of the lungs.