Natural perseitol is to be named D-perseitol because it was synthesized through the reduction of D-manno-D-gala-heptose. D-perseitol would surely result also from the reduction of L-gala-D-manno-heptose. It was demonstrated that perseitol with a configuration of the hydroxyl group at the 4th carbon atom corresponding to that of mannoheptulose showed a significant inhibition of glucokinase. A complex of perseitol (D-glycero-D-galacto-heptitol) and K+ ions, isolated from the leaves of Scurrula fusca (Loranthaceae), which has been traditionally used for the treatment of cancer in Sulawesi Island (Indonesia), exhibits a potent inhibitory effect on [3H]-leucine incorporation for protein synthesis in Ehrlich ascites tumor cells in mice. Transaldolase-deficient patients had subtle elevations of perseitol in urine. Thus, heptitol perseitol might serves as novel urinary biomarkers for identification of transaldolase deficiency.