The structure and sequence of the gene (DD/BABP) encoding a human dihydrodiol dehydrogenase/bile acid-binding protein (DD/BABP) were determined by analysis of genomic clones. Several overlapping clones containing parts of the gene were isolated from a lambda EMBL3 SP6/T7 library and characterized by restriction mapping and DNA sequencing. The gene spans approx. 16kb and consists of nine exons. The sizes of the exons range from 77 to 167 bp, whereas the intron sizes range from 375 to 3430 bp. The transcription start point (tsp) is located at -56 bp of the first ATG codon, as determined by primer extension. Neither a TATA box nor a CAT box was found upstream from the tsp. Southern blot analysis of the human genomic DNA, using the cDNA as the probe, revealed several additional hybridizing DNA bands, suggesting the existence of multiple related genes.