An animal model induced by striatal quinolinic acid (QA) injection shows ongoing striatal degeneration mimicking Huntington's disease. To study the migratory ability and the neuroprotective effect of human neural stem cells (NSCs) in this model, we transplanted NSCs (5 x 10(6)) or saline intravenously at 7 days after unilateral QA injection. NSCs-group exhibited the reduced apomorphine-induced rotation and the reduced striatal atrophy compared to the control. PCR analysis for the human-specific ERV-3 gene supported an evidence of the engraftment of human NSCs in the rat brain. X-gal+ cells were found in and around the damaged striatum and migrated NSCs differentiated into neurons and glias. This result indicates that intravenously injected human NSCs can migrate into the striatal lesion, decrease the following striatal atrophy, and induce long-term functional improvement in a glutamate toxicity-induced striatal degeneration model.