The GeneChip Canine Genome Array is the first available commercial canine expression array and contains 23,836 probe sets representing over 21,500 Canis familiaris transcripts. By providing comprehensive coverage of the Canis familiaris genome, the GeneChip Canine Genome Array represents an important development for the pharmaceutical industry to accelerate and advance toxicology and pharmaceutical research, including biomarker discovery, toxicity, and safety studies. Sequence information for the GeneChip Canine Genome Array includes public content from GenBank (release 137.0, August 2003), dbEST (October 2003), and proprietary beagle sequence content licensed from LION bioscience AG. LION bioscience sequence information was derived from sequences in cDNA libraries for the following eleven tissues: testis, ovary, brain, embryo, liver, spleen, kidney, muscle, aorta, uterus, and jejunum.