Mesenchymal dysplasia (mes) is a new autosomal recessive mouse mutation that alters normal growth of mesenchyme-derived tissues and provides a new mouse model for studying connective tissue development and defects. Mutants are characterized by preaxial polydactyly of all four feet, a shortened face, wide set eyes, domed head, and a shortened kinky tail. Multiple skeletal defects are seen in alizarin-stained specimens. Histological, areas of mineralization are found in tendons. Mutants also have increased musculature in the shoulders and hips and decreased peritoneal fat. Salivary glands, testes, and kidneys are smaller than in littermates. Mesenchymal dysplasia has been mapped to mouse chromosome (Chr) 13. These mapping crosses also confirmed that the Purkinje cell degeneration (pcd) mutation is on Chr 13.