OBJECTIVES: I. Determine the biochemical modulation dose l of O6-benzylguanine (BG), defined as the dose at which baseline O6-alkylguanine DNA alkyltransferase (AGT) activity in circulating peripheral blood mononuclear cells (PBMC) decreases by greater than 90% in patients with advanced solid tumors at 2 hours after BG infusion. II. Determine the biochemical modulation dose t/18 (BMDt/18) of BG, defined as the dose at which AGT activity in human metastatic tumor tissue decreases to undetectable levels at 18 hours after BG infusion. III. Determine the maximum tolerated dose of carmustine (BCNU) when administered with BG at the BMDt/18 in these patients. IV. Determine the toxicities of BG and BCNU in these patients. V. Determine the pharmacokinetic parameters of BG administered at the BMDt/18, and determine any effects of BCNU on BG pharmacokinetics. VI. Assess any antitumor response in patients with metastatic solid tumors treated with this regimen. VII. Determine the effect of lower, more frequent bolus doses or a continuous infusion of BG on the depletion of AGT activity in PBMC and tumor tissue in these patients. VIII. Determine the pharmacokinetics of BG in lower, more frequent bolus doses or continuous infusion.