Stem cells can differentiate into all of the specialized embryonic tissues during embryo development. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing specialized cells, in order to maintain the normal turnover of regenerative organs, such as blood, skin or intestinal tissues. Recent studies suggest that maintenance and differentiation of stem cells are regulated by microRNAs (miRNA). MiRNAs are small single-stranded RNA molecules (~20nt long), playing an important role in gene regulation and cell differentiation. MiRNAs are found to be differentially expressed in stem cells, such as brain-specific miR-124a and miR-9 molecules during neural lineage differentiation. In addition, miRNAs are also reported to regulate cancer stem cells. Signosis has developed a miRNA array specifically to target 47 miRNAs that are shown in literature to be associated with stem cell differentiation and maintenance. The array can be used for human, mouse and rat samples. Profiling the expression of these miRNAs will help to reveal the functions of miRNAs in stem cells.