The purpose of the present study was to determine the efficacy of boron neutron capture therapy (BNCT) in treating the therapeutically refractory F98 glioma, using boronophenylalanine (BPA) as the capture agent. F98 glioma cells (10(5)) were implanted stereotactically into the brains of Fischer rats and 15 days later the animals were injected intraperitoneally with 897 mg/kg of D,L-BPA. Between 3 and 9 h after administration blood and tumor boron concentrations exhibited monoexponential decay with half-lives (t1/2) of 4.3 and 5.3 h, respectively. When 803 mg/kg of 10B-L-BPA was administered, the tumor 10B concentration was 29.4 micrograms/g and tumor-to-blood and tumor-to-brain ratios were 3.5 and 3.9, respectively. Seven days after intracerebral implantation of 10(5) F98 cells, BNCT was initiated at the Brookhaven Medical Research Reactor. The median survival time for irradiated controls (no BPA), which had received tumor physical doses of 1.7, 2.6 or 3.5 Gy, were 27, 33 and 38 days, respectively, compared to 24 days for untreated rats (P < or = 0.025-0.0001). The median survival time for BNCT-treated groups that had received 803 mg/kg of 10B-L-BPA 6 h prior to irradiation with total estimated tumor physical doses of 5.7, 8.6 and 11.5 Gy were 32, 37 and 59 days, respectively. Although the enhanced median survival times of two of the BNCT-treated group (8.6 and 11.5 Gy) were significant compared to their matched irradiated controls (P < or = 0.0175-0.0277), all BNCT-treated animals died in less than 160 days. It remains to be determined whether better survival can be achieved using higher doses of BPA and neutrons to treat a tumor, which at this time cannot be cured by any therapeutic modality.