<p>[Introduction] A low concentration of dexamethasone (DEX) is added to the hepatocyte culture medium to maintain morphology and improve liver function. However, DEX, which is a glucocorticoid receptor ligand, induces the CYPs expression. In drug safety and pharmacokinetic tests, drug-drug interactions may occur even at low concentrations of DEX. In this study, human cryopreserved hepatocytes (cryoheps) were cultured in a commercially available hepatocyte maintenance medium (HM medium) with or without DEX, and the effects of DEX on the expression of major CYPs were examined. Furthermore, a condition for improving CYPs metabolism was studied in a medium without DEX. Sakai et al. reported that hepatocytes cultured on plastic plates were not supplied with sufficient oxygen compared to in vivo. Therefore, we attempted to improve CYPs metabolism by using the InnoCell^TM T-plate (InnoCell; Mitsui Chemicals, Inc.), which is an oxygen-permeable cell culture vessel. [Methods] Cryoheps from vendor A were cultured in HM medium from vendor B with or without DEX, and the major CYPs (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4) expression levels were compared. In addition, in conditions without DEX, cells were cultured on InnoCell, and the expression and activity of major CYPs were compared with those cultured on plastic plates. [Results and Conclusion] CYP3A4 expression level was decreased in the condition without DEX. In contrast, expression levels of CYPs other than CYP3A4 were not changed significantly. CYP3A4 expression level was increased to the same level as in human liver by improving oxygenation in conditions without DEX. In addition, improving oxygenation did not significantly alter CYP1A2 expression, but increased CYP1A activity. These results suggest that cryoheps have enough CYP activity even in medium without DEX by the improved oxygenation.</p>