Dimensional changes of asbestos bodies and uncoated fibers and the leaching of magnesium from the surface of chrysotile after a single intratracheal injection (1 mg) were investigated in male hamsters.  The animals were sacrificed at 1 day, 6 months, 1 and 2 years later.  In addition to histopathological observation, asbestos tissue burdens were investigated in 25 micrometer thick sections of the lungs.  The sections were ashed in a low-temperature asher to be extracted with a carbon film.  The carbon extracted ashed sections were investigated by high resolution analytical electron microscopy to characterize asbestos fibers and asbestos bodies.  Pulmonary interstitial and pleural fibrosis were observed after 6 months and later.  Light microscopically, asbestos bodies were observed at 6 months; their incidence subsequently increased with the lapse of time after the injection.  Asbestos bodies measured on light micrographs became longer with the lapse of time.  This suggested that coating of chrysotile fibers had been continuously progressing in the lung.  Geometric means of length and width of uncoated chrysotile fibers seen by transmission electron microscopy in animals at 1 year (length; 1.4 micrometer, width; 0.057 micrometer) or 2 years (1.2 micrometer, 0.047 micrometer) were greater compared with those of animals at 1 day (0.9 micrometer, 0.041 micrometer) or 6 months (0.9 micrometer, 0.037 micrometer) after instillation.  These findings suggested that short and thin chrysotile fibers were cleared from the lung.  Energy dispersive X-ray spectrometry revealed that the ratio of the content of magnesium to that of silicon was slightly lower in the fibers detected in the animals with a recovery period of 6 months and longer (6-12%), suggesting that magnesium had been leaching from the surface of chrysotile fibers although its amount was small.