TIGR and Affymetrix are pleased to report the recent completion of the Arabidopsis whole genome Affymetrix GeneChipâ that has been developed as part of the TIGR reannotation effort (see also http://www.corporate-ir.net/ireye/ir_site.zhtml?ticker=AFFX&script=410&layout=-6&item_id=278919). The design takes advantage of recent developments in the Affymetrix GeneChipâ technology that incorporate reductions in both feature size and the number of probe pairs per gene. This allowed us to place ~22,700 probe sets on the new array. To best represent the >26,000 annotated genes, precedence was given to genes for which either expression evidence or a credible database match exist. Among the remaining "hypothetical" genes, we nominated every singleton and at least one member of each paralogous family. We also chose to represent very closely related gene pairs by a single probe set, thus allowing us to incorporate an additional ~1,000 genes. Altogether, the new ATH1 array represents ~24,000 genes. A list of these genes can be found at the TIGR ftp site (ftp://ftp.tigr.org/pub/data/a_thaliana/ath1/Arabdiopsis_microarray_geneListing.txt). Affymetrix will make the array available to the research community in two phases. At this time, and until full QC is completed, Affymetrix is accepting orders only for whole Made to Order lots (80-90 probe arrays) which will be ready in mid-May. Following full QC, the arrays will become available as a commercial, fully supported Affymetrix product (packs of 5 and 30 probe arrays) in late summer.