Cytochrome p450 3A4 (CYP3A4) plays an important role in drug metabolism, and the enzymatic activity of CYP3A4 contributes to many adverse drug-drug interactions. Here we describe a transgenic mouse model that is useful in monitoring the in vivo transcriptional regulation of the human CYP3A4 gene. A reporter construct consisting of 13 kilobases of the human CYP3A4 promoter controlling the firefly luciferase gene was used to generate a transgenic mouse line [FVB/N-Tg(CYP3A4-luc)Xen]. Reporter gene expression was assessed using an in vivo imaging system (IVIS) in anesthetized mice. Basal expression of the reporter was highest in liver and kidney, and moderate in the duodenum in male transgenic mice, whereas the basal luciferase activity was highest in the duodenum and lower in kidney and liver in females. Injections of pregnenolone, phenobarbital, rifampicin, nifedipine, dexamethasone, 5-pregnen-3beta-ol-20-one-16alpha-carbonitrile (PCN), and clotrimazole resulted in a time-dependent induction of luciferase expression, primarily in liver, that peaked at 6 h post injection. The greatest induction was found with clotrimazole, dexamethasone, and PCN, whereas the lowest induction followed pregnenolone, phenobarbital, and rifampicin injection. In general, male mice responded to these drugs more strongly than did females. Our results suggest that the human CYP3A4 promoter functions in transgenic mice and that this in vivo model can be used to study transcriptional regulation of the CYP3A4 gene.