Unsupervised hierarchical clustering of the normal human tissues based on the variation of miRNA expression correlates with the anatomical locations and physiological functions of the tissues. Normalized CT for each assay was transformed into ΔCT against the average CT of all assays examined and clustered after mean-centering the data for each miRNA but no centering was done for the tissues. A detailed view of the clustering patterns of normal tissues is on the right. The blue bar on the left side of the heat map represented the group of miRNAs primarily expressed in placenta, and the red bar indicated the miRNAs with significant increased expression in epithelial tissues including the gastrointestinal organs. A pseudocolor scale bar represented the fold change relative to the mean of the data for each miRNA.