ABSTRACT. A novel canine tumor cell line designated as the CMS-C cell line was established from pleomorphic rhabdomyosarcoma (RMS) raised in the prostate gland of a 14-year-old intact male mixed-breed dog. CMS-C cells displayed the same immunohistochemical characteristics (positive for vimentin and desmin and negative for cytokeratin and smooth muscle actin) as the original tumor cells and express myoD1 and UCP3, known as striated muscle-specific molecules, as shown by RT-PCR assay. Therefore, the established CMS-C cell line appears to be of rhabdomyoblast cell origin. The CMS-C cell line established from pleomorphic RMS will be a useful tool for further studies about canine RMS.