The purpose of this study was to determine the levels of whole tissue, cytosolic, and mitochondrial glutathione in the tissue zones of the rat kidney. Reduced (GSH) and oxidized glutathione (GSSG) were measured spectrophotometrically in tissue homogenates. Differential centrifugation was used to isolate the cytosolic and mitochondrial fractions. Cortical GSH and GSSG levels accounted for 51% and 60%, respectively, of the GSH and GSSG levels in the whole kidney. Cytosolic GSH levels were similar in the cortex and medulla but lower in the papilla. Cytosolic GSSG levels were highest in the cortex and lowest in the medulla. Mitochondrial GSH and GSSG levels did not follow a pattern similar to that of the cytosol or whole tissue. The mitochondrial redox ratio (GSH/GSH + GSSG X 100) was significantly higher in the cortex (ie., 67%) than the medulla (ie., 39%). The cytosolic redox ratio showed an opposite relationship with the cortex (ie., 57%) being lower than the medulla (ie., 78%). This study demonstrates that there are differences in GSH levels, GSSG levels, and the redox ratio in the tissue zones of the rat kidney. / Department of Physiology and Health Science