The purpose of this study was to evaluate the effect of basic fibroblastic growth factor (bFGF) on the growth of human UM-MB1 medulloblastoma xenografts injected intracranially in nude mice. Under general anesthesia, a homogenous suspension of UM-MB1 cells (10(5)/10 microl) were injected in the caudoputamen nuclei of the right cerebral hemisphere using a stereotaxic apparatus. The treatment group (n = 9) received 10 microl of a bFGF solution (20 microg/ml) at 3 and 6 days following the inoculation of the cells at the injection site using the same stereotaxic coordinates. The control group (n = 9) were injected intracranially with a phosphate-buffered saline vehicle using a similar protocol. Mice were sacrificed 3 weeks following the xenograft surgery and the brains were prepared for histological observations as well as tumor volume evaluations. The mean volume of bFGF-treated tumors (mean volume +/- SD = 50.0 +/- 32.9 +/- mm3) was significantly smaller than for the non-treated xenografts (mean volume +/- SD = 199.0 +/- 42.1 mm3) (t-test, p < 0.001). Compared to non-treated tumor cells, bFGF-treated medulloblastoma cells had a greater cytoplasm volume and their nuclei contained more euchromatin suggesting that bFGF may initiate differentiation. In conclusion, our results suggest that bFGF may offer a new chemotherapeutic modality for the treatment of medulloblastoma.