. This paper predicted their potential toxicity to human using bronchoalveolar lavage technique on the basis of comparisons with positive reference materials (quartz and chrysotile) and negative reference materials (titanium dioxide and alumina (SAFFIL) fibre). All rats dosed with dust showed some increase in lung weight relative to the saline control, though the only significant differences were seen between the rats dosed with quartz or chrysotile and those dosed with saline. From the morphological observation of lavage cells, a benign reaction of macrophages to CF and CFC was observed, whereas a series of changes in macrophages was involved in rats dosed with quartz and chrysotile. CF and CFC did not induce a significant increase in the total cell count or percentages of neutrophils and lymphocytes in bronchoalveolar lavage. The two materials tested had much lower toxicity than that of quartz and chrysotile, and were comparable with the effect induced by titanium dioxide and SAFFIL fibre which had minimal toxicity. The present work provides a scientific basis for the setting of occupational health standards for carbon fibre and carbon fibre composite dust in the workplace. (J Occup Health 2001; 43: 75-79)