The differences between the properties of nanomaterials and bulk materials generate uncertainty for measuring the genotoxic potential of nanomaterials using current genotoxicity assays. There is only a limited amount of data relating to the toxicity and genotoxicity of nanomaterials and, in some cases, the data are inconclusive or outright contradictory. From a regulatory standpoint, it is important to determine if the current genotoxicity assays used to evaluate the safety of new products are adequate for detecting the potential toxicity and/or genotoxicity of nanomaterials.