The Rice Expression Profile Database (RiceXPro) is a repository of gene expression profiles derived from microarray analysis of tissues/organs encompassing the entire growth of the rice plant under natural field conditions, rice seedlings treated with various phytohormones, and specific cell types/tissues isolated by laser microdissection (LMD). This database is part of a project on rice transcriptome analysis using microarray technology aimed at characterizing the expression profile of all predicted genes in rice and providing reference information that can be used in functional genomics. All expression profiles were generated using a single microarray platform with probes based on manually curated gene models in RAP-DB and rice full-length cDNA sequence information in KOME database. This project is supported by a grant from the Ministry of Agriculture, Forestry and Fisheries of Japan.