Abstract Summary: Rice (Oryza sativa L.) is an important model monocot and cereal crop. While the rice genome sequence has been published and annotated, relatively little is known about the transcriptional networks that regulate rice gene expression. For this reason, we have developed Osiris, a database containing promoter sequences, predicted transcription factor (TF) binding sites, gene ontology annotation and microarray expression data for 24 209 genes in the rice genome. These tools are seamlessly integrated in the Osiris web site, allowing the user to visualize TF binding sites in multiple promoters; analyze the statistical significance of enriched TF binding sites; query for genes containing similar promoter regulatory logic or gene function and visualize the microarray expression patterns of queried or selected gene sets. Availability: http://www.bioinformatics2.wsu.edu/Osiris Contact: jwyrick@wsu.edu Supplementary information: Supplementary data are available at Bioinformatics online.