The human stromelysin 3 (STMY3) gene, a new member of the matrix metalloproteinase (MMP) gene family, may contribute to breast cancer cell invasion, and has been localized by in situ hybridization to the long arm of chromosome 22. As demonstrated using a panel of somatic cell hybrids, the STMY3 gene is in band 22q11.2, in close proximity to the BCR gene involved in chronic myeloid leukemia, but far from the (11;22) translocation breakpoint observed in Ewing sarcoma. This position differs from that reported on chromosomes 11 and 16 for the other MMP genes, suggesting that stromelysin 3 could be a member of a new MMP subfamily.