A cDNA of coagulation Factor IX gene has been screened from the $lambda$gt11 human fetal liver cDNA library, and used to construct a 2.8-kb full length cDNA after recombining with the N-terminal fragment from pTZ-FIX. Human genomic DNA was isolated, digested with the restriction endonucleases, TaqI, EcoRI, and HindIII, and Southern hybridization was performed using the full length factor IX cDNA as a probe. The hybridized bands generated by the restriction endonucleases were the followings: TaqI, 0.3, 1.0, 1.6, 1.8, 2.7, 3.7, and 5.3 kb bands; EcoRI, 1.8, 4.8, 4.9, 5.5, 6.8, and 12.6 kb bands; HindIII, 4.1, 4.4, 5.2, 5.8, 7.6, and 12.5 kb bands. When the Southern bands were physically mapped along the genome, about 50-kb continuous region harboring almost all of the genomic region of Factor Ⅸ gene was covered. These results suggest a possibility of using an exonal cDNA probe to diagnose abnormalities including large deletions, insertions, and rearrangements along the genome, if there is any.