A starch-gel electrophoretic study of 2 peripheral blood lymphocyte enzymes, phosphoglucomutase (PGM) and adenylate kinase (AK), was performed in 25 donor-recipient allogenic bone marrow transplantation (BMT) pairs. A different isoenzymatic pattern between donor and recipient for PGM, AK or both, was observed in 11 of these 25 pairs. From these 11 cases, an identical donor isoenzyme pattern was observed in 10 cases between 24 and 85 days (mean 41.8, SD 22.08) after BM infusion confirming engraftment, whereas in the remaining 1 the demonstration could not be substantiated due to early death. The present study demonstrates that, in addition to other cell markers, the simultaneous study of PGM and AK isoenzymes allows confirmation of BM engraftment in about 45% of cases, much earlier than is possible by means of red cell antigen analysis. Moreover, it is a simple, relatively inexpensive and rapid laboratory tool for a better characterization of the established chimera.