Variable Number of Tandem Repeats (VNTR) DNA polymorphisms analysis was used in bone marrow transplantation (BMT) follow up. Three Acute Myeloid Leukemia (AML) transplants were investigated with YNH 24/MspI and with EFD 64.2/Rsa or HinfI highly polymorphic VNTRs. Absence of mosaicism and complete engraftment of donor cells was observed in two cases, while mixed hematopoietic chimerism was present in a case in which T cell depleted marrow was transplanted. VNTR systems represent accurate and sensitive individual specific markers for monitoring the clinical course of patients undergoing BMT, and for detecting the biological origin of relapses.