Previous light microscopic analysis of lung tissue from persons living close to a large open-pit asbestos mine demonstrated asbestos body counts intermediate between those of referents and those of miners and millers. In this study, we examined via electron microscopy and x-ray energy dispersive spectrometry autopsy lung specimens from individuals ascertained to be environmentally or occupationally exposed and from a referent group. Environmental group concentrations of chrysotile fibers longer than 5 microns were significantly higher than those of referents, and 50% lower than those observed in the occupational group. Tremolite was markedly increased in the occupational group, but only marginally greater in the environmentally exposed. Electron-microscopy-derived concentrations of amphibole fibers longer than 5 microns correlated well with light microscopic asbestos body counts in the occupational group but not in the environmental or referent groups. Chrysotile concentration was not related to asbestos body concentration in any group. Crocidolite fiber, a commercial amphibole not native to the region, was nonetheless identified in lung tissue from 15 of 23 chrysotile miners and millers. Environmental exposure to asbestos fiber as a result of residence within 40 km of the mines results in increased lung chrysotile content.