Sir, In haematopoietic transplantation, myeloid and megakaryocytic engraftment typically occurs in tandem at a median of 15 days (range = 5–41 days). Various factors, including the age of the recipient, stem cell dose (CD34+ cells), source of stem cells (bone marrow versus mobilized blood stem cells), degree of HLA matching, administration of colony stimulating factors, T cell depletion and infections, are known to affect the process of engraftment. Vancomycin is commonly used during the course of haematopoietic transplantation. Although vancomycin-induced neutropenia has been reported, in the presence of other confounding factors such as infection, sepsis and other antibiotics, a direct causal relationship may be difficult to establish. We herein report a case of rapid megakaryocytic engraftment with normalization of platelet counts in the absence of myeloid engraftment and restoration of myeloid haematopoiesis following discontinuation of vancomycin. A 59-year-old male received a non-myeloablative allogeneic haematopoietic stem cell transplant (allo-SCT) for intermediate risk (normal cytogenetics) acute myelogenous leukaemia (AML-M4) in first complete remission (CR1) from a 6/6 HLAmatched unrelated donor. A total of 6.1 · 10 CD34+ cells were infused following sub-ablative conditioning (busulfan 0.8 mg/kg every 6 h · 2 days, fludarabine 30 mg/m · 3 days and alemtuzumab 10 mg · 5 days). Graft versus host disease (GVHD) prophylaxis was performed with a short course of methotrexate (10 mg/m on day +1; 5 mg/m on day +3; and 5 mg/m on day +6) and tacrolimus. The transplant course was uncomplicated except for a catheter-insertion-site infection on day +12, for which intravenous vancomycin (1 g every 12 h) was initiated. The peak and trough vancomycin levels were 27.1 mg/L (range = 30.0– 40.0 mg/L) and 8.4 mg/L (range = 5.0–10.0 mg/L), respectively. The patient remained afebrile, blood cultures were negative and he did not receive any other antibiotic. Figure 1 demonstrates the neutrophil and platelet nadir along with the haematopoietic reconstitution. Megakaryocytic engraftment (platelets >20 000/dL · 3 consecutive days in the absence of transfusion) occurred on day +10 without myeloid engraftment. On day +18 colony stimulating factor (G-CSF; 480 mg subcutaneously daily) was initiated. On day +19 the platelet count was 160 000/dL without any evidence of myeloid engraftment (neutrophils = 2, WBC = 100/dL). On day +21, vancomycin was discontinued; myeloid engraftment occurred on day +23 (13 days after megakaryocytic engraftment). An absolute lymphocyte count (ALC) at myeloid engraftment was 18 cells/mm. Lymphocyte recovery (ALC ‡ 500 cells/mm) occurred in 70 days. Engraftment studies on day 30 confirmed 99.5% donor chimerism. Pre-emptive ganciclovir was initiated for cytomegalovirus (CMV) antigenaemia on day 21; the patient had no CMV disease. Currently, at 6 months post-transplantation, he has no evidence of GVHD. Megakaryocytic engraftment on day +10 and complete platelet recovery (platelets >150 000/dL) by day +19 in the absence of myeloid engraftment provides evidence supporting the occurrence of granulocytopenia associated with vancomycin therapy. A previous report had described vancomycin-associated granulocytopenia after successful engraftment following an auto-transplant. A bone marrow specimen obtained at the time of neutropenia demonstrated in vitro suppression of progenitor cell growth at increasing concentrations of vancomycin. The patient represents the first published case of vancomycinassociated failed myeloid engraftment.