Tubular organization and vascular-tubular relations were studied by double injection in canine kidneys. Blood vessels were injected via the artery after perfusion fixation. Tubules were injected by micropipettes inserted into the urinary spaces of selected glomeruli in cleared slices. One hundred proximal convoluted tubules, 16 Henle loops, and 5 distal convoluted tubules were defined. Only subcapsular proximal convolutions were perfused by efferent vessels arising from the same glomerulus (43 of 55). In midcortex, proximal convolutions were generally perfused over less than half their length by the parent efferent (21 of 31). Here tubules entirely perfused by the parent efferent were rare (2 of 31). No inner cortical proximal convolutions were perfused by the efferent from the same glomerulus (0 of 14). Henle's loops were found to be perfused by the efferents of many glomeruli regardless of the cortical position of the parent glomerulus. Distal convolutions shared the perfusion of proximal convolutions of the same glomerulus. Thus, each nephron is apparently functionally dependent on efferent blood from glomeruli of many other nephrons. New synoptic diagrams of canine renal organization are presented.