1. In bilaterally nephrectomized rats, 24 or 44 +/- 2 h after surgery, normal distribution of tissue pO2 values was measured at the surface of liver and thigh muscles. 2. As cardiac output was generally higher in uremic rats as compared with that of corresponding controls and arterial pO2 was rather elevated in the uremic rats, it may be concluded that the cells of the uremic animals were sufficiently supplied with oxygen. 3. Consequently, the known depression of whole body oxygen consumption in acute uremic rats must be due to metabolic defects at the cellular level. 4. Elevated arterial blood pressure in acute uremic rats is due to elevated cardiac output which in turn is mainly caused by fluid retention. When uremic rats are deprived of water the increase of blood pressure, cardiac output and plasma volume are considerably blunted.