A new xenotransplantable tumor line, MED-FU, was derived from a 6-year-old female patient with cerebellar medulloblastoma. This tumor was grown in nude mice as serially transplantable subcutaneous xenografts composed of small round cells with hyperchromatic nuclei and scant cytoplasm. Many rosettes and mitoses were observed. Immunohistochemically, glial fibrillary acidic protein (GFAP), S-100 protein, and neuron specific enolase (NSE) were not detected. The doubling time of the subcutaneous tumors was 6.8 days. Highly concentrated polyamines were detected in the tumor tissue and serum of tumor-bearing mice. This xenotransplanted tumor line, MED-FU, is considered to provide an available experimental model for the study of human medulloblastoma.