A study carried out on the mortality of over 3700 individuals who worked in a factory making railway rolling stock, in which crocidolite was used to insulate the coaches from the end of 50's to the end of 70's, was summarized. The clinical data, checked by best evidence method, show that the pleural plaques on HRCT are the best indicator of past asbestos exposure rather than asbestos bodies or free asbestos fibers in BAL.