ABSTRACT A group of 135 ex-employees of the Quebec chrysotile production industry comprising men who were born between 1901 and 1920, who had left the industry between 1950 and 1961, and had been radiographed before leaving, attended in 1972 for a medical examination and further chest radiograph. This report concerns 86 men whose withdrawal film was within 12 months of leaving and who had not been exposed subsequently to asbestos or other fibrogenic dust. Seven separate assessments were made of the paired radiographs, side by side in known temporal order. The assessments were classified as showing 'increse' or 'no change'. In 66 film-pairs from men with two years' employment or longer, at least four assessments were of parenchymal increase in six, of pleural increase in 13, and of both parenchymal and pleural increase in two, total 21 (or 31%). There was similar agreement of no change in 24 pairs (36%), and evidence was equivocal in the remaining 21 pairs. Parenchymal increase was not agreed in any of the 20 film-pairs from men with shorter employment, but pleural increase was seen in four of these men, a proportion similar to that in those exposed longer. We conclude that the parenchymal changes observed after leaving the industry, most of which were 'attacks' rather than 'progression', were attributable to the earlier occupational exposure to chrysotile; there were no important differences in age or smoking habit between those with and without parenchymal change.
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