The luminal aspect of intrarenal arteries and veins in the rat has been investigated by scanning electron microscopy (SEM). The endothelium of the intrarenal arteries consists of spindle-shaped cells and forms longitudinally running ridges which correlate with the folding pattern of the underlying internal elastic lamina. Intraarterial "cushions" were found at the origins of afferent arterioles from arcuate arteries and along the entire course of interlobular arteries. The intrarenal veins are made up of a thin, extensively fenestrated epithelium equal to that of peritubular capillaries. The outer aspect of the endothelium contacts adjacent tubules as closely as the capillaries proper. Thereby, the luminal aspect of the veins exhibits a striking "tubule relief" created by the underlying tubules. This wall structure of the intrarenal veins suggest that diameter and shape of the veins are probably highly dependent on the surrounding interstitial pressure.