Two genomic clones containing the 3'-end of CYP3A7, the whole 5'-flanking region plus the first exon of CYP3A5 were isolated from two different human genomic banks and sequenced. The 5'-flanking region of CYP3A5, from nucleotide -1 to -1434, was 60% and 59% similar with the corresponding regions of CYP3A4 and CYP3A7, respectively. However, the similarity increased to 74% when regions from nucleotide -1 to -700 were compared and dropped to less than 42% for regions upstream from -700. The CYP3A5 promoter contains a CATA box instead of the typical TATA box and a basic transcription element (BTE). Other consensus sequences previously found in CYP3A4 and CYP3A7 were also identified in the 5'-flanking of CYP3A5 from -1 to -700. Both CYP3A5 and CYP3A7 genes appear to be tandemly associated and transcribed in the same direction on chromosome 7.