An important measure to ensure successful follow-up in patients with allogeneic stem cell transplant is to evaluate for engraftment. Recent studies have shown that detecting minimal residual disease is important in order to predict early clinical relapse. We followed 88 leukemic patients with pre- and posttransplant Wilms tumor gene (WT1) levels to predict relapse and variable number of tandem repeats (VNTR) for engraftment. We have found that high pretransplant WT1 levels correlated significantly with relapse in all patient groups, but more significantly in the acute nonlymphoblastic leukemia (ANLL) patients. Posttransplant WT1 level correlated with VNTR status such that low WT1 is associated invariably with VNTR of 100% donor origin, while high WT1 is associated with VNTR of 20%. The association is significant in all patients, specifically in ANLL patients. In this preliminary study, we demonstrate that patients harboring detectable levels of WT1 prior to stem cell transplant have a higher chance of relapse, and posttransplant WT1 and VNTR status appeared to be dependent parameters predicting relapse when present in the posttransplant period. By combining 2 highly sensitive molecular techniques, we have found that this combined technique provided us with a promising alternative for overcoming the limitations imposed by each separate procedure. More studies are necessary before we can come to any significant conclusions.