We further evaluated the liver toxicity of nano-TiO2. Using light microscopy, we found that there was no significant change in the liver of mice exposed to low dose (i.p. for 14 days, 5 mg/kg) nano-TiO2 (Fig. 4a, b). We observed marked vascular obstruction and dilation (Fig. (Fig.4c,4c, 50 mg/kg), increases in basophils (Fig. (Fig.4d,4d, 100 mg/kg), partial ischemia in the liver (Fig. (Fig.4e,4e, 150 mg/kg), and obstruction of central veins (Fig. (Fig.4f,4f, 200 mg/kg) in mice exposed to nano-TiO2 (i.p.).