The miRNA Isolation Kits are designed for the purification of microRNA (miRNA) and other small cellular RNAs from tissue samples and cultured cells. Purification of miRNA allows research into significant biological pathways for gene regulation. The standard protocol for isolating total RNA and miRNA are not optimized for small RNA molecules, and therefore result in the loss of substantial amounts of miRNA and other small RNA. In addition, the removal of the predominantly larger RNAs is required for accurate analysis of miRNA expression by qPCR or microarray analysis. These kits are specifically designed for the purification of small RNA with minimal contamination from large RNA molecules or genomic DNA. The method employs a spin column with a silica-based filter matrix that binds RNA in the presence of a chaotropic salt. This method is based on the selective binding of RNA molecules of various sizes to the silica-based fiber matrix when different ethanol concentrations are present in the solvent.