OUTLINE: This is a dose escalation study. Patients receive a single dose of O6-benzylguanine (O6-BG) IV over 1 hour at one of two dose levels. Patients undergo surgery 16-20 hours after administration of O6-BG. Up to 13 patients receive the lower dose level of O6-BG. If more than 3 patients have detectable AGT levels, additional patients receive the higher dose. The optimal biologic dose (OBD) is defined as the lowest dose level at which at least 11 of 13 patients have AGT activity less than 10 fmol/mg protein after O6-BG dosing. Patients are followed at 1 and 3 weeks post surgery.