We have karyotyped a human giant cell glioblastoma removed from an 11-year-old girl and have established from it a subcutaneously transplantable line in athymic nude mice. The original tumor contained near-haploid cells with 25 or 26 chromosomes, including two copies of #1, (7 or 7p+) and #18. There were also hyperdiploid (49-52) cells that were tetraploid for these same three chromosome types; doubled versions of the hyperdiploid population were also seen. The stemline of the mouse-grown tumor was 26,X, +1, +7p+, +18 in the first passage and has remained consistently near-haploid through ten serial in vivo passages. Growth stabilization has occurred with an average latency of less than 3 months. This transplantable line is available for evaluating chemotherapeutic responsiveness of human giant cell glioblastoma and for studying near-haploidy in solid human tumors.