This study reports that dexamethasone (DEX) significantly induces CYP3A11, CYP3A13 and CYP3A25 mRNA expression in male and female 4 days, 3 weeks and 18 weeks old C57BL/6J mice. Furthermore, CYP3A activity, as measured by erythromycin-N-demethylation, is also significantly increased. PXR, RXRα and CAR are known to be involved in the induction of CYP3As. Here we report nuclear receptors PXR and RXRα but not CAR demonstrate gender- and age-dependent expression. Also, treatment of C57BL/6J mice with DEX induces PXR but not RXRα or CAR. In summary, we demonstrate DEX is not only able to up-regulate CYP3A expression and activity, but also the nuclear receptor PXR through which it may exert this effect. Furthermore, the gender- and age-dependent pattern of basal PXR and RXRα expression is similar to the 3 CYP3As analysed.