The inert gas washout technique of Thorburn et al. has been adapted to the rat. The left kidney was exposed and placed in a micropuncture type lead spoon. A lead ring, a fenestrated lead lid and a suitable collimator absorbed all radioactivity coming from outside the left kidney. Injections of 133xenon were made through a polyethylene aortic catheter. The washout of the radioactive indicator gas was monitored with a 2-inch crystal detector placed above the exposed kidney. By means of 85krypton autoradiography the 4 single exponential components of the washout curve of the normal rat kidney were identified with 4 vascular zones of the kidney: the cortex + subcortical area (CP I), the outer medulla (CP II), the inner medulla (CP III) and the hilar fat (CP IV). The following normal values were found for the intrarenal distribution of blood flow (IDBF) and for the local blood flow rates (Fi): 81.7% of total renal blood flow are supplied to CP I, 11.6% to CP II, 3.8% to CP II and 2.7% to CP IV. Local blood flow rates (in ml/min, g of tissue) were 5.21 in CP I, 0.79 in CP II, 0.09 in CP III and 0.13 in CP IV. As compared with other species no significant differences occur in IDBF nor local blood flow rates.