Tissues obtained at autopsy or biopsy from 81 workers and 2 household persons, were chemically digested. The asbestos fibres recovered were characterized by analytical transmission electron microscopy. Among the 83 causes of death were 33 mesotheliomas, 35 lung cancers, 12 asbestosis and 3 from other cancers. Of the three major commercial asbestos fibre types, amosite was found to be the most prevalent fibre, occurring in approximately 76% of the cases, followed by chrysotile in approximately 60% and crocidolite in approximately 24%. Amosite and chrysotile were observed as the single commercial fibre in approximately 22 and approximately 17% of the cases respectively, whereas crocidolite and tremolite were found as the single fibre type in only approximately 2.5% of the cases. Among the fifteen cases where chrysotile and tremolite occurred together, the amount of chrysotile fibre always exceeded tremolite. However, tremolite was also found in ten additional cases where chrysotile was not detected. Amosite was present in four, amosite plus crocidolite in three, and crocidolite alone in one. Amosite was present in all of the insulation workers' lungs studied and was found in the highest concentration in this exposure category. The highest chrysotile concentration was found among workers in general trades. Although most prevalent in shipyard workers lungs, crocidolite concentration is not statistically different among the exposure groups studied. Although crocidolite was found in twenty cases, amosite accompanied it in eighteen of these. Eleven of the 20 cases were from shipyard workers. Of the 8 mesothelioma cases, 7 also contained amosite. Crocidolite alone only occurred in 1 of the 33 mesothelioma cases analysed. We concluded the following: crocidolite exposure occurred among USA insulators and a large percentage of other workers as well; insulation workers are primarily exposed to amosite; mixed fibre exposures are associated with more mesotheliomas than single fibre exposures; chrysotile only exposure is associated with approximately 12% of the mesothelioma cases studied; and if tremolite exposure is associated with chrysotile exposure, the chrysotile amount exceeds that for the associated tremolite.