Tumor fragments from glioblastoma multiforme patients were obtained during surgery. Tissue specimens were taken from viable tumor areas that corresponded to regions with contrast enhancement on preoperative MRI-scans. The specimens were transferred to test tubes containing complete growth medium, and spheroids were prepared as previously described [20] . The same method was applied for tumor material passaged in nude rats. Briefly, tissue samples were minced into ,0.5 mm fragments and placed into 80 cm 2 tissue culture flasks (Nunc, Roskilde, Denmark) base-coated with 0.75% agar (Difco, Detroit, MI). The spheroids were maintained in a standard tissue culture incubator with 5% CO 2 and 100% relative humidity at 37uC. The medium was changed once a week. Spheroids with diameters between 400 and 600 mm were selected for in vitro experiments and for intracerebral implantation.