Pressure in the interlobular arteries (Pila) in the rat kidney was measured by micropuncture after acute ablation of a slice of the renal cortex. The interlobular arteries (ILA) were identified by intra-aortic injection of 25 µm microspheres, which embolized in the ILA mainly in the outer third of the cortex. Measurements proximal to the arrested spheres showed an average pressure drop of 32mmHg between the aorta and the punctured ILA, locating about 50% of the preglomerular resistance proximal to the afferent arteriole. Spontaneous, interindividual differences in mean arterial pressure in the range of 91-125mmHg were not associated with a consistent change in Pila, while lower aortic pressures seemed to be associated with almost proportional lowering of Pila-