The present study investigated effects of human umbilical cord blood derived CD34+ cells on sensorimotor, cognitive, and histological outcome in rats following focal cerebral ischemia. Halothane anesthetized adult male Wistar rats were subjected to transient or permanent occlusion of the middle cerebral artery (MCAO) followed by intravenous administration of CD34+ cells (5 x 10(5) or 2 x 10(6)) after 24 h recovery. The beam-walking and cylinder tests were used to assess sensorimotor function, and Morris water-maze examined cognitive performance during a 25 day follow-up period. Subsequently, rats were perfused for measurement of infarct volumes and detection of CD34' cells in the brain by immunohistochemistry (MAB1281). MCAO rats showed minor or no spontaneous recovery in sensorimotor function during the follow-up. The recovery profile was similar in MCAO controls and in MCAO rats that received CD34+ cells, although CD34+ cells seemed to improve the use of impaired forelimb. There was also a trend toward improved water-maze performance by CD34+ cells in transient MCAO rats. Infarct volumes assessed from Nissl-stained sections on postoperative day 25 did not differ between the experimental groups. MAB 1281-positive cells were not detected in the brain of MCAO rats that received CD34+ cells. The present study suggests that CD34+ cells might improve functional outcome in MCAO rats after systemic administration, but do not significantly provide neuroprotection.