14C]AZQ (2-4 mg/m 2, 100 200 mCi) was administered at varying times to five patients undergoing surgical resection of intracerebral tumors. Plasma, cerebrospinal fluid (CSF), edematous brain, and tumor specimens were obtained during surgery and the concentration of AZQ was determined radiochemically and chromatographically. Total [14C]AZQ equivalent concentration in tumor for two patients was determined to be 47.5% and 85% of concurrent plasma concentration which was similar to that found in normal brain (60.4% and 75.5% respectively). Only 18 45% of the total radioactivity in tumor tissue and 30 56% in plasma were accounted for by unchanged AZQ. These findings suggest that AZQ may be metabolized to a certain extent. Tissue samples from various organs were obtained during autopsy in a patient who expired ten days after AZQ administration. The highest AZQ concentration was found in the liver, followed by the kidney. Comparable amounts were found in normal brain and brain tumor (22 ng/g vs. 31 ng/g respectively). These results indicate that AZQ penetrates readily into the normal brain and brain tumor with a tendency to persist. * PCNU -l-(2-chloroethyl)-3-(2,6-dioxo-3-piperidyl)-l-nitrosourea. ** DDP = Cis-diamminedichloroplatinum (I1).