Two year rodent bioassays play a key role in the assessment of carcinogenic potential of chemicals to humans. The seventh amendment to the European Cosmetics Directive will ban in 2013 the marketing of cosmetic and personal care products that contain ingredients that have been tested in animal models. Thus 2-year rodent bioassays will not be available for cosmetics/personal care products. Furthermore, for large testing programs like REACH, in vivo carcinogenicity testing is impractical. Alternative ways to carcinogenicity assessment are urgently required. In terms of standardization and validation, the most advanced in vitro tests for carcinogenicity are the cell transformation assays (CTAs). Although CTAs do not mimic the whole carcinogenesis process in vivo, they represent a valuable support in identifying transforming potential of chemicals. CTAs have been shown to detect genotoxic as well as non-genotoxic carcinogens and are helpful in the determination of thresholds for genotoxic and non-genotoxic carcinogens. The extensive review on CTAs by the OECD (OECD (2007) Environmental Health and Safety Publications, Series on Testing and Assessment, No. 31) and the proven within- and between-laboratories reproducibility of the SHE CTAs justifies broader use of these methods to assess carcinogenic potential of chemicals.