Primary hepatocytes are functional units with complete cellular structure. With complete nuclear and cytoplasmic components, it can complete the transcription, translation, protein localization and exercise of metabolic enzyme activities. Primary hepatocytes are widely used in phase I metabolism, phase II metabolism test, induction test, cell-based inhibition test and hepatocyte toxicity test, inhibition of drug transporters on hepatocytes surface and substrate test. The convenience and reproducibility of human liver cells frozen in liquid nitrogen make them an ideal tool for predicting human metabolism and transporter studies as specified in the latest FDA guidelines.