Because of their self-renewal and pluripotency properties, human embryonic stem cells (hES) receive a marked attention from scientists and clinicians for regenerative medicine. The most recent application of hES cells may however reside in their use as a tool in drug development. The currently available cellular models for preclinical testing consist in primary and immortalized cells that display limitations in terms of available amount and likeliness to their in vivo counterparts, respectively. hES cells have the potential to revolutionize drug discovery by providing a physiological model for any human cell type in the desired amount for the earliest steps of drug development, notably for pharmacological, metabolic and toxicity evaluation. This new generation of model may contribute to reduce, refine or replace animal testing and decrease drug attrition.