This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goal of this protocol is to develop a system for efficiently screening new agents for potential use in Phase I and II brain tumor clinical trials by directly determining if these drugs can cross the BBB in patients with brain tumors. The plan is to place a microdialysis catheter into either the tumor or adjacent cerebral cortex when a brain tumor patient undergoes a biopsy or debulking craniotomy. Once the patient has recovered from the anesthesia and is stable post-operatively, s/he will be given a dose of a systemic chemotherapy agent (in this feasibility study temozolomide, a drug already known to cross the BBB, will be used), and intracerebral microdialysis will be performed to determine if any of the drug is recovered in the dialysate, reflecting the degree to which the drug is able to penetrate the BBB. Drug levels in the brain tumor interstitium will be compared to levels in the plasma.