Radiolabelling of BCNU by C-11 or N-13 has provided a means of mapping, with PET sequential scans, the entry, distribution, and persistence of this drug in Grade III and IV human gliomas. Our preliminary findings indicate that the differential uptake of the drug is greater in the tumor than in a control area of brain, and that it also has a different clearance half-life. PET mapping following supra-selective intracerebral arterial infusion of BCNU has shown significant reduction, and in one case almost total disappearance of the tumor. More detailed studies using PET and experimental radioautography of radio-labelled BCNU, AspCNU, and SarCNU will be made. The resulting information would improve the scientific basis and methodology of administration of drugs now available. It would also provide a model for evaluating new drugs. The metabolic information derived from PET scanning of gliomas would help to correlate these chemical and biological activity and provide a means of early detection of tumor response to chemotherapy and radiotherapy.