The GeneChip Chicken Genome Array contains comprehensive coverage of 32,773 transcripts corresponding to over 28,000 chicken genes. The Chicken Genome Array also contains 689 probe sets for detecting 684 transcripts from 17 avian viruses. The GeneChip Chicken Genome Array is a key research tool for the study of chicken genomics and chicken viral pathogens. Chicken is an ideal model organism for studying developmental biology, as embryonic development occurs in ovo rather than in utero, providing an easily accessible way for researchers to study stages of embryonic development. Sequence information for this array includes public content from GenBank, UniGene Build 18 (May 2004), and 28,416 predicted genes from the Ensembl annotation effort of the complete chicken genome (version 1, released May 2004).