The GeneChip Test3 arrays provide a convenient and accurate means of determining the quality of labeled target prior to analysis on other GeneChip expression arrays. Test3 arrays contain probe sets representing a subset of characterized genes from various organisms, including mammals, plants, and eubacteria. Additionally, the GeneChip Test3 Array contains a subset of human and mouse housekeeping genes shown to be expressed early on in fetal development and throughout adulthood. The arrays also serve as an economically priced training tool for new GeneChip product users. Please refer to www.affymetrix.com for more information on Test3 array formats.