The genotoxic potential of a high purity sample of single-wall carbon nanotubes (SWCNTs) was evaluated using a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse mutation test (Ames test), an in vitro chromosomal aberration test, and an in vivo mouse bone marrow micronucleus test. The SWCNTs exerted no genotoxicity in Salmonella typhimurium TA97, TA98, TA100, and TA1535, or in Escherichia coli WP2 uvrA/pKM101, whether in the absence or presence of metabolic activation and at concentrations of 12.5–500μg/plate. In the chromosomal aberration test, at 300–1000μg/mL, the SWCNTs did not increase the number of structural or numerical chromosomal aberrations, whether the test was conducted with or without metabolic activation. In the in vivo bone marrow micronucleus test, doses of 60mg/kg and 200mg/kg SWCNTs did not affect the proportions of immature and total erythrocytes, nor did it increase the number of micronuclei in the immature erythrocytes of mice. The results of these studies show that the high purity and well-dispersed sample of SWCNTs are not genotoxic under the conditions of the in vitro bacterial reverse mutation assay, chromosomal aberration assay, or in vivo bone marrow micronucleus test, and thus appear not to pose a genotoxic risk to human health in vivo.