Hepatocytes represent an important tool for the investigation of species differences in drug metabolism and toxicity. Data obtained with hepatocytes from multiple animal species, including man, allow better prediction of the effects of xenobiotics in man. Cryopreservation of hepatocytes extends the use of this important experimental system by enhancing the convenience of its use. Also, it allows the researchers to perform experiments not plausible with freshly isolated hepatocytes, such as the direct comparison of xenobiotic toxicity and metabolism in hepatocytes from multiple human donors in a single experiment.