In vivo rodent models remain the only reliable way for experimental investigation of the carcinogenic risk of chemicals to humans, however, the rodent carcinogenicity assay is expensive and time-consuming. Several in vitro alternatives to animal-based methods have been developed. Among these methods, cell transformation assays (CTA), which mimic some stages of in vivo multistep carcinogenesis, have been proposed for predicting carcinogenic potential of chemicals. This document focuses on the three main in vitro CTAs, the SHE, the BALB/c 3T3 and the C3H10T1/2 assays. The SHE assay uses karyotypically normal cells and is believed to detect early steps of carcinogenesis. The other two assays are based on immortalized aneuploid cell lines which measure later stages of carcinogenesis.