Abstract The glyoxylate-cycle system in germinated sesame seed embryos was examined from several viewpoints. This glyoxylate-cycle system was found in the mitochondrial fraction of germinated sesame seed embryos, and it also was found that this cycle should predominate over the TCA-cycle system in seed mitochondria during the germination, although the mitochondrial fraction of sesame seed also contained other TCA-cycle enzymes, condensing enzyme, aconitase, fumarase, etc., in addition to isocitritase and malate synthetase. The activities of both glyoxylate-cycle enzymes, isocitritase and malate synthetase, were increased remarkably by the period of seed germination after radicle emergency, and reached maximum activities at near the 8th day of seed germination. From these data and other information in the literature, the glyoxylate-cycle system in sesame seed embryos should act as a plausible route for the conversion of acetate into nucleic acid by means of some modified metabolic pathway combined with reversal of glycolysis.