As another component of the study with uf TiO2, female Wistar rats were exposed to high-purity furnace carbon black (particle size -= 14 nm, specific surface area = 227 m2/g), MMAD = 0.64 mm). The extractable organic mass of the furnace black was 0.04%; the content of benzo[a]pyrene was 0.6 pg/mg and that of 1-nitropyrene was < 0.5 ng/mg particle mass. Rats were exposed in whole-body exposure chambers for 18 h/d, 5 days/wk to 7.4 mg/m3 CB for 4 months followed by 12.2 mg/m3 for 20 months. After exposure, the rats were kept in clean air for another 6 months. The incidence of benign and malignant lung tumours was increased in the treated groups after 30 months.