All new chemicals are tested for their potential to cause DNA damage (genotoxicity), as this is linked to cancer. A tiered approach is used, with the chemicals first being tested in vitro. Those that induce DNA damage (test positives) are then usually tested again using animals. Some genotoxic agents give positive results in vitro at relatively high doses, but do not cause DNA damage at low doses more typical of human exposure levels. Identifying the dose below which DNA damage does not occur is important because understanding how this relates to human exposure levels can provide an opportunity to avoid using animals. This project will use an in vitro system to assess the genotoxic potential for a wide range of chemicals, helping to establish optimum testing strategies for evaluating the effects of dose and potentially reducing animal use.