Eight mouse gene loci (Atp1b2, Epo, Kit, Krt2, Mor1, Ren1, Pdgfb, and Wnt1) that contain unidentified microsatellites were selected to detect simple sequence-length polymorphisms on genomic DNAs from two laboratory strains (C57BL/6J and RF/J) and strains recently derived from the Mus musculus species complex (CAST/Ei, MOLF/Ei, CZECH II, and M. m. domesticus) and from M. spretus (SPRET/Ei). All microsatellite DNA sequences varied in size among some of the seven mouse strains tested. These new polymorphisms might be useful in the search for tumor suppressor genes involved in specific cancers.