The finding of stem/progenitor cells in postnatal bone marrow and umbilical cord blood, opens up a possibility of using stem cells to treat neurologic diseases. There is a controversy, whether intravenously administered human umbilical cord blood cells (HUCBC) migrate to the brain, differentiate and improve recovery after ischemia. In this study, 1-3 x10;6 cells from non-cultured (non-committed) mononuclear HUCBC fraction were intravenously infused 1, 2, 3 or 7 days after a transient middle cerebral artery occlusion (MCAo) in adult rats. We found few human cells only in the ischemic area, localized mostly around blood vessels with few positive cells in the brain parenchyma. Timing of HUCBC delivery after ischemia or injection of Cyclosporin A at the time of delivery, had no effect on the number of human cells detected in the ischemic brain. Infusion of HUCBC did not reduce infarct volume and did not improve neurologic deficits after MCAo, suggesting that HUCBC failed to migrate/survive in the ischemic brain and did not provide significant neurological benefits.