Inhalation of asbestos may be associated with increased risk of developing malignant neoplasms. Some of the fibers become coated in the lung, resulting in "asbestos bodies." The occurrence of structures with the appearance of asbestos bodies in the lungs of urban dwellers the world over, individuals with no known exposure to these mineral fibers, has raised the question of whether the community at large may also have increased risk of neoplasia as the result of chance environmental asbestos exposure. Since other fibrous materials may also sometimes become so coated, epidemiology evaluation of the presence of asbestos bodies has been hampered by difficulties in obtaining absolute identification of the cores of the bodies found. Five fibrous silicates, consisting of four amphiboles (amosite, anthophyllite, crocidolite and tremolite) and one serpentine (chrysotile), constitute the asbestos mineral group. Chemically, they are diverse enough for unique identification. The electron microprobe analyzer permits microchemical analysis of particles in the sublight microscopic size range. Analysis of asbestos body cores requires particle selection, extraction from tissue matrix, a suitable conducting substrate, proper coating material, selection of optimal instrumental operating conditions and comparison of unknown cores with known fiber standards. In this investigation, asbestos body cores have been analyzed from tissues obtained from occupationally exposed individuals (known fiber exposure), laboratory animals (known exposure) and individuals with no known occupational exposure. Cores of bodies have been analyzed as amosite, chrysotile, chemically degraded chrysotile and cores of undetermined nature. Amosite fibers as cores of asbestos bodies show no marked chemical degradation even after prolonged biologic residence, whereas chrysotile asbestos cores are markedly degraded. Cores of asbestos bodies from the general population, from individuals with no known exposure, may consist of degraded chrysotile, synthetic silicate fibers and, in some cases, amphibole asbestos.