Microsatellites are regions of DNA repeats with different lengths, i.e., instability, highlighting DNA mismatch repair gene deficiencies. Typical lengths for these DNA repeats are between 1-6 base pairs and vary person to person such that each person has a set length of these microsatellites in their genome. Measurements of MSI have traditionally been performed using qPCR/CE analysis methods, but new methodologies are now available that includes digital droplet PCR (ddPCR) as well as Next Generation Sequencing (NGS). Microsatellite instability status has been linked to favorable outcomes in I-O treatment response by patients with diseases such as Lynch Syndrome and colorectal cancer. Hence MSI measurements have become an important biomarker in immuno-oncology therapeutics. LGC SeraCare has developed microsatellite instability (MSI) reference materials containing the key mono- and dinucleotide biomarkers typically analyzed in molecular MSI assays – NR-21, NR-24, BAT-25, BAT-26 and MONO-27. These markers are blended at two different allele frequency levels – AF5% and AF20% - to support MSI assay LoD determinations and accurate MSI detection. These products are offered as tumor-normal matched pairs, with variants precisely quantitated by digital PCR as well as qPCR/CE against a highly characterized genomic DNA from a background WT cell line (GM24385) determined as microsatellite stable (MSS).