In a previous study of discrete segments of rat nephron, we reported the levels of high-energy adenylate and guanylate phosphates to be highest in the distal straight and convoluted tubules. Those findings stimulated the study of the distribution of seven enzymes involved in the following metabolic pathways of these nucleotides [Formula: see text]. The patterns of distribution of enzymes in each pathway differed greatly. The phosphodiesterases, 1 and 2, were high in glomeruli and distal tubular segments and low in proximal segments. Adenylate kinase, 3, in contrast, was high in glomeruli, proximal segments, thick ascending limb of Henle, and distal convoluted tubules. Guanylate kinase levels, 4, however, were similar in all segments. The pattern of nucleosidediphosphate kinase, 5, was high in proximal convoluted, thick ascending limb, and distal convoluted tubules. The pattern of the degradative enzyme, 5'-nucleotidase, 6, whose levels were highest in proximal segments, was opposite from that of AMP deaminase, 7, highest in the distal nephrons. These dissimilar patterns underscore the extent of nephron heterogeneity.