The genotoxicity of single-walled carbon nanotubes (SWCNTs) was determined using a battery of genotoxicity assays, comprising a bacterial reverse mutation test, an in vitro mammalian chromosomal aberration test and a mammalian erythrocytes micronucleus test. SWCNTs had no mutagenicity in S. typhimurium TA98, TA100, TA1535 or TA1537, or in E. coli WP2uvrA, in the absence or presence of metabolic activation. SWCNTs did not increase the number of structural or numerical chromosomal aberrations after short-term or continuous exposure. In the micronucleus test using CD-1 mice, SWCNTs did not affect the proportion of immature erythrocytes, the total proportion of erythrocytes or the number of micronuclei in immature erythrocytes. SWCNTs appear not to pose a genotoxic risk. Copyright © 2012 John Wiley & Sons, Ltd.