A new continuous cell line and transplantable xenograft, D283 Med, was derived from the peritoneal implant and ascitic fluid of a child with metastatic medulloblastoma and grew in vitro in suspension culture with spontaneous macroscopic spheroid formation. The in vitro population doubling time was 52.55 hours. Mean colony forming efficiency in an agarose medium was 1.83 +/- 0.56%. The cell line, D283 Med, grew in athymic mice as serially transplantable intracranial and subcutaneous xenografts. Intracranial tumors grew as masses of small cells with scant cytoplasm and abundant mitotic figures and prominent anuclear zones resembling neuroblastic rosettes. Subcutaneous (SQ) tumors were markedly cellular neoplasms but did not contain rosettes. They expressed glutamine synthetase, neuron-specific enolase and neurofilament protein. Glial fibrillary acidic protein and S-100 protein were not detected. The SQ tumors grew to 500 mm3 with a latency of 52.55 +/- 12.5 days and a doubling time of 9.33 +/- 2.39 days. The stemline karyotypes of the peritoneal implant and ascitic fluid cells contained an extra copy of chromosome number 11 and three marker chromosomes (8q+, 17p+, 20q+). The cultured cell line and subcutaneous and intracranial xenografts retained the three marker chromosomes and differed from the original karyotype only in that they lacked the additional copy of chromosome number 11. This cell line and transplantable xenograft may allow further analysis of the biological properties and therapeutic sensitivity of human medulloblastoma.