The wide-spread use of microarray technologies to study plant transcriptomes has Ied to important discoveries and to an accumulation of profiling data covering a wide range of different tissues,developmental stages,perturbations,and genotypes.Querying a large number of microarray experiments can provide insights that cannot be gained by analyzing single experiments.However,such a meta-analysis poses.significant challenges with respect to data comparability and normalization,systematic sample annotation,and analysis tools.Genevestigator addresses these issues using a large curated expression database and a set of specifically developed analysis tools that are accessible over the inteet.This combination has already proven to be usefuIin the area of plant research based on a Iarge set of Arabidopsis data (Grennan,2006).Here,we present the release of the Genevestigator rice and barley gene expression databases that contain quailty-controlled and welI annotated microarray experiments using ontologies.The databases currently comprise experiments from pathology,plant nutrition.abiotic stress,hormone treatment,genotype,and spatial or temporal analysis,but are expected to cover a broad variety of research areas as more experimentaI data become available.The transcriptome meta-analysis of the modeI species rice and barley iS expected to deliver results that can be used for functional genomics and biotechnoIogical applications in cereals.