The broad aim underlying the present research was to investigate the distribution and homing of bone marrow-derived macrophages in a rodent model of transient middle cerebral artery occlusion using MRI and ultrasmall superparamagnetic iron oxide (USPIO) to magnetically label bone marrow-derived macrophages. The specific aim was to assess the intra-carotid infusion route for bone marrow-derived macrophage delivery at reperfusion. Fifteen Sprague-Dawley rats sustained 1 h of middle cerebral artery occlusion. USPIO-labeled bone marrow-derived macrophages were slowly injected for 5 min immediately after reperfusion in ischemic animals (n=7), 1 h after the end of surgery in sham animals (n=5) and very shortly after anesthesia in healthy animals (n=3). Multiparametric MRI was performed at day 0, just after cell administration, and repeated at day 1. Immunohistological analysis included Prussian blue for iron detection and rat endothelial cell antigen-1 for endothelium visualization. Intra-carotid cell delivery brought a large number of cells to the ipsilateral hemisphere of the brain, as seen on both MRI and immunohistology. However, it was associated with high mortality (50%). The study of sham animals demonstrated that intra-carotid cell delivery could induce ischemic lesions and may thus favor additional brain damage. The present study highlights severe drawbacks to the intra-carotid delivery of macrophages at the time of reperfusion in this rodent model of transient cerebral ischemia. Multiparametric MRI appears to be a method of choice to monitor longitudinally the effects of cell infusion, allowing the assessment of both cell fate with the help of magnetic labeling and of potential tissue damage.