Genetically defined rodent strains with stable phenotypes require periodic genetic characterization to ensure strain/line purity prior to extensive research or breeding programs. Analysis of specific microsatellite locations on each chromosome is used for background strain characterization and estimating genetic variation/drift among individuals. Our PCR-based method scans the X chromosome and all 19 autosomes of the mouse genome at approximately 15 cM intervals. We have panels in place for more than a dozen common inbred strains and routinely develop new panels to meet custom requests. Additionally, rat and zebrafish microsatellite panels with complete genome coverage are available. Our background strain characterization can also be used to assess allele frequencies, heterozygosity, and relatedness in outbred populations, or for mapping and fine mapping applications.