ArrayExpress is a public repository for microarray gene expression data hosted at the European Bioinformatics Institute (EBI). It supports the MIAME standards and stores well-annotated raw and normalized data. As of November 2004, it contains data from approximately 12,000 hybridizations covering 35 species. Data can be submitted online or from local databases or LIMS in a standard format. Password-protected access is provided for reviewers and authors. Data can be retrieved by accession number or queried by species, author, or array platform. A query facility for gene and sample properties is available for curated data. Data can be visualized and analyzed using Expression Profiler, an integrated tool. ArrayExpress is available at http://www.ebi.ac.uk/arrayexpress. ArrayExpress supports standards developed by the Microarray Gene Expression Data (MGED) society, including MIAME and MAGE-ML. It is one of three repositories recommended by MGED for storing data related to publications. The ArrayExpress suite includes MIAMExpress, a web-based data submission tool; the ArrayExpress repository; a query-optimized data warehouse; and Expression Profiler. All software is open source. As the number of journals requiring public repository submissions increases, the volume of data in ArrayExpress is growing rapidly. During the last 12 months, the content has grown more than 10-fold. The repository contains approximately 12,000 hybridizations from 35 species, with most studies involving Homo sapiens or Mus musculus. Over 25% of experiments use Affymetrix arrays. While most experiments study gene expression, there is a growing volume of ChIP-on-Chip and Comparative Genome Hybridization data. ArrayExpress has two submission routes: online via MIAMExpress or via a MAGE-ML-based pipeline. MIAMExpress is open source and can be customized. The curation team processes submissions, ensuring MIAME compliance, data accuracy, and completeness. Data are owned by the submitter and released on specified dates or upon publication. Custom-made arrays are submitted as tab-delimited files. The ArrayExpress data warehouse supports queries on gene and sample attributes. It is based on BioMart technology and includes gene annotations, GO terms, and InterPro terms. The data warehouse is used to store curated data, and the repository is integrated with EBI services. Future developments include automated curation and integration with databases like UniProt and Ensembl via DAS.ArrayExpress is a public repository for microarray gene expression data hosted at the European Bioinformatics Institute (EBI). It supports the MIAME standards and stores well-annotated raw and normalized data. As of November 2004, it contains data from approximately 12,000 hybridizations covering 35 species. Data can be submitted online or from local databases or LIMS in a standard format. Password-protected access is provided for reviewers and authors. Data can be retrieved by accession number or queried by species, author, or array platform. A query facility for gene and sample properties is available for curated data. Data can be visualized and analyzed using Expression Profiler, an integrated tool. ArrayExpress is available at http://www.ebi.ac.uk/arrayexpress. ArrayExpress supports standards developed by the Microarray Gene Expression Data (MGED) society, including MIAME and MAGE-ML. It is one of three repositories recommended by MGED for storing data related to publications. The ArrayExpress suite includes MIAMExpress, a web-based data submission tool; the ArrayExpress repository; a query-optimized data warehouse; and Expression Profiler. All software is open source. As the number of journals requiring public repository submissions increases, the volume of data in ArrayExpress is growing rapidly. During the last 12 months, the content has grown more than 10-fold. The repository contains approximately 12,000 hybridizations from 35 species, with most studies involving Homo sapiens or Mus musculus. Over 25% of experiments use Affymetrix arrays. While most experiments study gene expression, there is a growing volume of ChIP-on-Chip and Comparative Genome Hybridization data. ArrayExpress has two submission routes: online via MIAMExpress or via a MAGE-ML-based pipeline. MIAMExpress is open source and can be customized. The curation team processes submissions, ensuring MIAME compliance, data accuracy, and completeness. Data are owned by the submitter and released on specified dates or upon publication. Custom-made arrays are submitted as tab-delimited files. The ArrayExpress data warehouse supports queries on gene and sample attributes. It is based on BioMart technology and includes gene annotations, GO terms, and InterPro terms. The data warehouse is used to store curated data, and the repository is integrated with EBI services. Future developments include automated curation and integration with databases like UniProt and Ensembl via DAS.