Asbestos fiber analysis in nine lung cancer cases with high asbestos exposure. 
We examined the types and sizes of 100 asbestos fibers in lung tissue obtained from 9 lung-cancer cases (5 autopsy and 4 surgical) with more than 10(4) asbestos bodies per 5 g of wet lung tissue, asbestos bodies in histological sections, and the history of occupational asbestos exposure.  Evaluation of asbestos fibers by transmission electron microscopy (2,000 x magnification) revealed that most fibers were longer than 3 microns (96%) and were thicker than 0.1 micron (93%).  The analytical conditions we used enabled us to identify 99.7% of all asbestos fibers as being amphibole asbestos.  Crocidolite fiber, which was found most frequently (73.1%), was the predominant type of fiber found in 8 of the 9 cases; crocidolite was followed by amosite (21.7%), which was the predominant type found in the remaining case.  Crocidolite fibers were thin and had a high aspect ratio (mean diameter = 0.23 micron, mean aspect ratio [length/diameter] = 85.5).  Amosite fibers were long, and they also had a high aspect ratio (mean length = 21.8 microns, mean aspect ratio = 66.4).  It has been suggested that such fibers with a high aspect ratio are strongly carcinogenic to pulmonary parenchyma.  Review of our previous and present data with respect to the ratio of amosite to crocidolite fibers in groups of subjects who had various diseases revealed that this ratio was relatively constant in some occupations.  The more predominant fibers found were crocidolite in insulation workers and amosite in railroad workers.  The ratio of amosite to crocidolite fibers should be considered in tissue-burden studies.