We evaluated effects of graft transport time on outcomes after transplantation of 938 unrelated donor bone marrow (BM) or 507 peripheral blood progenitor cells (PBPC) in patients with acute or chronic leukemia and myelodysplastic syndrome (MDS). BM grafts were collected at 107 centers and PBPC, 89 centers. Median time from end of collection to infusion was 14 hours for BM and 15 hours for PBPC. Platelet recovery was less likely in BM recipients when the interval from end of collection to receipt at transplant center was >or=20 hours (odds ratio 0.47, P = .010) and when the interval from receipt to infusion was >or=6 hours (odds ratio 0.57, P = .001). Mortality rates were higher in recipients of HLA-matched BM when the interval from end of collection to receipt at transplant center was >or=20 hours (relative risk 2.67, P < .001) after adjustment for other significant prognostic factors. Mortality after HLA-mismatched BM transplants was not associated with transport time. Transport times had no demonstrable effect on outcomes after PBPC transplants. These data support a general review of current transport procedures, especially for BM grafts requiring longer transport time and every effort made to minimize time from collection to infusion.