Let-7 family is known to regulate proliferation and differentiation processes in species ranging from C- elegans to human. The mature forms (designated let-7a through let-7i ) differ at one to four positions from the let-7a sequence. The expression level of the isoforms is variable, which may play a diverse role in organ development and disease etiology. To distinguish these isoforms will help to elicit the mechanism of Let-7 function. Based on its proprietary technology, Signosis has developed a highly sensitive and discriminative real-time PCR assay method for measuring miRNA expression of let-7 isoforms (Let-7a, Let-7b, Let-7c, Let-7d, Let-7e, Let-7f, Let-7g and Let-7i) simultaneously. The assay implements oligo-ligation and SYBR green based real-time PCR, which can be used for quantitative analysis of miRNA expression in either total RNA or cell lysate without cDNA conversion. Each kit allows for 12 reactions.