The volume of the intravenously injected solution was 50 μl. The mass (concentration) of thin-MWCNTs and thick-MWCNTs were 0.02 mg (0.4 mg/ml) in the high-dose group and 0.002 mg (0.04 mg/ml) in the low-dose group. This concentration corresponds to approximately 0.7 mg and 0.07 mg per kg body weight, respectively. Four groups consisting of low- and high-doses in each of the two MWCNTs groups were administered in rasH2 mice, in addition to a negative control that was administered with polysorbate 80 alone (vehicle group) for a total of five groups. There were 16 animals in the thick-MWCNTs (low-dose) and thick-MWCNTs (high-dose) groups, while the other three groups included 15 animals for a total of 77 animals.