Predicting how a drug will behave in humans before clinical testing requires a battery of sophisticated in vitro tests that complement traditional expensive in vivo safety assessments. In vitro assays attempt to mimic in vivo conditions but always involve an element of uncertainty. One approach to solving this problem has been the use of in vitro screens to identify early on the characteristics of a new chemical entity (NCE), particularly with the respect to its metabolism. Early drug metabolism models help predict a compound's elimination from the body, or metabolic stability, which affects its duration of action. More elaborate in vitro models can identify which enzyme systems play a role in elimination, which help predict drug-drug interactions, as well as the potential for the compound of interest to induce enzyme systems to eliminate other drugs. Finally, experimental design, standardized assays and assay conditions allow researchers to pool data and develop new predictive models. This meeting will concentrate on the advantages and disadvantages of various in vitro systems to characterize the metabolic fate of the NCE in question and prioritize compound selection for further development.