The invention relates to the generation of non-human transgenic animals comprising a reporter construct for producing a detectable amount of a reporter molecule operably linked to a transcriptional regulatory nucleic acid molecule from the human CYP3A4 gene located between the initiation of transcription site of the gene and a position located 13,000 nucleotides upstream from the site. The invention also relates to the use of these animals for determining the effect of a compound, particularly, but not exclusively, a xenobiotic or steroid, on the regulation of expression of the CYP3A4 gene in a human.