RefEx (Reference Expression dataset; http://refex.dbcls.jp) provides suitable datasets as a reference for gene expression data from 40 normal human, mouse, and rat tissues and cells. Forty tissues were selected based on the experience gained while constructing the bodymap database. The 40 tissues are classified into 10 groups (i.e., brain, blood, connective, reproductive, muscular, alimentary, liver, lung, urinary, and endo/exocrine). These groupings are mainly used for the abstraction of the gene expression profiles in the summary view and the inference of gene functions by the gene expression profiles. The following four different measurement strategies were used in our collected gene expression data: ESTs, Affymetrix GeneChip, CAGE, and RNA-Seq. These four types of data were linked based on the NCBI gene IDs in the dataset in RefEx.