Traditionally animal experiments are used to assess the toxicological safety of chemicals. An alternative to this is the use of in vitro toxicity tests, but these assays do not always reflect in vivo toxicity values. Translation of in vitro data to the in vivo situation is therefore an important, but still limiting step for the use of in vitro toxicity outcomes in the regulatory safety assessment of chemicals. In the present thesis we demonstrate how we can translate in vitro embryotoxicity data to in vivo developmental toxicity values for rat and human using physiologically based kinetic (PBK) models, which mathematically describe the absorption, distribution, metabolism and excretion (ADME) of a compound in an organism. Additionally, we demonstrate a modelling approach that integrates in vitro toxicity data, PBK modelling and Monte Carlo simulations to predict the effects of human interindividual variation in kinetics for phenol induced development toxicity. Altogether, this thesis may contribute to the replacement of animal studies for the safety testing of chemicals, and may lead towards an approach that is cheaper, non-animal based and more directly relevant for humans.