The canine gastin gene was isolated from a genomic library. Screening of about 500,000 recombinant phages was carried out by in situ plaque hybridization employing a canine gastrin cDNA clone as a probe. As a result two different genomic clones were obtained. These contain 13-kb and 15-kb genomic DNA fragments that share at least 11-kb DNA. Comparison of the determined genomic sequences with the cDNA sequence revealed the structure of three exons and two introns, which comprise 2.3 kb in total. It resembles the human gastrin gene structure. However, the canine intron I is only 1.7 kb long, about half the size of the human intron I.