Since their invention in the late 1980s, microarrays have revolutionized our understanding of gene expression patterns and the important role transcription plays in human health and disease. As the popularity of high-throughput hybridization arrays has increased over the years, the publicâ€™s demand for access to original array datasets has increased as well. In response to this demand, the National Center for Biotechnology Information (NCBI) established the Gene Expression Omnibus (GEO) in 2000, which can be accessed at http://www.ncbi. nlm.nih.gov/geo . Two years later, the European Bioinformatics Institute (EBI) established ArrayExpress, which can be accessed at http://www.ebi.ac.uk/Arrayexpress . Currently, these repositories hold over 1 million samples combined. Recent updates on both the GEO and ArrayExpress repositories were published earlier this year [3,4].