Soybean (Glycine max) nodules formed by inoculation with either an effective strain or an ineffective (noninvasive, noduleforming) strain of Bradyrhizobium japonicum were assayed for changes in developmental patterns of carbon metabolic enzymes of the plant nodule cells. Of the enzyme activities measured, only sucrose synthase, glutamine synthetase, and alcohol dehydrogenase were altered in the ineffective nodules relative to the effective nodules. Sucrose synthase and glutamine synthetase activities were greatly reduced, whereas alcohol dehydrogenase activity was elevated. Dark-induced senescence severely affected sucrose synthase but had little, if any, effect on the other enzymes measured. The developmental pattems of the anaerobically induced enzymes, aldolase and alcohol dehydrogenase, were different from those expected, implying that their development is not regulated solely by oxygen deprivation. However, anaerobic treatment of nodules resulted in responses similar to those enzymes in maize. The developmental profiles of the carbon metabolic enzymes suggest that carbohydrates are metabolized via the sucrose synthase and pentose phosphate pathways. This route of carbon metabolism, compared to glycolysis, would reduce the requirement of ATP for carbohydrate catabolism, generate NADPH for biosynthetic reactions, and provide intermediates for plant secondary metabolism.The establishment of an effective N2 symbiosis on the roots of leguminous plants requires infection by the appropriate species ofRhizobium. The Rhizobium/leguminous plant nodule provides a unique environment where photosynthetically derived carbon compounds synthesized by the plant are exchanged for ammonium derived from the reduction of atmospheric N2 catalyzed within the bacterial endophytes. Nodule differentiation results in a variety of morphological (22) and biochemical (15,18,27) changes in the plant nodule cells to accommodate the energy needs of the N2 fixation process and to supply carbon skeletons to transport the ammonium formed via nitrogenase.