Recent advances in the field of red cell enzyme anomalies are reviewed with a stress on G6PD as a genetic marker and on hereditary hemolytic anemia due to red cell enzyme anomalies. Using G6PD as a genetic marker, most benign and malignant tumors have been shown to have a clonal origin, except for neurofibroma and veneral warts which are clearly polyclonal. Recently, the primary structure of human red cell phosphoglycerate kinase was clarified and moreover, single amino acid substitutions of four mutant phosphoglycerate kinases were determined. To accomplish this, a method which requires only 20 ml of blood has been developed. It is a consensus among investigators in this field that the pathogenesis in three-quarters of the congenital nonspherocytic hemolytic anemia patients remain unknown even after adequate red cell enzyme studies which are now available, as well as Carrell's isopropanol test for the detection of unstable hemoglobins.