Prescreening of blood cells of prospective donors and hosts by simple electrophoresis for well-known polymorphic enzyme phenotypes offers markers to monitor the fate of bone marrow grafts in the hosts. Cellogel electrophoresis is handy for routine screening of red cell enzymes for polymorphic variants [Rattazzi et al, 1967; Meera Khan and Rattazzi, 1968; Meera Khan, 1971; Someren et al, 1974; Ebeli-Struijk et al, 1976; Meera Khan and Doppert, 1976; Meera Khan et al, 1982]. Highly sensitive methods for microelectrophoretic assays for phenotyping the individual enzyme systems, if they become available, will be of greater value than the conventional procedures. For PGM1 phenotyping, the procedure of isoelectric-focusing (IEF) [Winter et al, 1977] was found to be highly sensitive and gave the best resolution. Polymorphic variants of house-keeping enzymes, by nature, can play the role of universal markers since they are expressed in individual types of the whole range of cells derived from hematopoietic and stromal cell precursors in the transplanted patients. Compared to chromosome analysis in dividing cells or screening for RFLP's detectable in unique DNA sequences, marker enzyme phenotyping by electrophoresis is methodologically simple, easy, quick, inexpensive, rapidly repeatable and equally reliable, requires only a small quantity of easily obtainable peripheral blood sample, and could monitor all lineages of blood cells including non-nucleated and nondividing cells.