The GeneChip Maize Genome Array has 17,555 probe sets to interrogate approximately 14,850 Zea mays transcripts, which represent 13,339 genes (12,113 of which are represented in distinct UniGene clusters).Zea mays is one of the most economically important crops in the world. The Maize Genome Array, through examination of gene expression patterns of Zea mays, will enable researchers to view the global transcription effects of external stimuli, such as fertilizers, pesticides, and growth conditions. This array provides comprehensive coverage of over 100 cultivars present in NCBI’s UniGene dataset, including the most highly represented strains: B73, Ohio43,W22, W23, W64A, and Black Mexican Sweet. The sequence information for this array was selected from NCBI’s GenBank (upto September 29, 2004) and Zea mays UniGene Build 42 (July 23,2004) databases. The Maize Genome Array was created within the Affymetrix GeneChip Consortia Program and provides scientists with a single array which can be used for gene expression studies in Zea mays.