MRI-guided stereotactic intraputaminal cell implantation into PD patients was performed using a Leksell Stereotactic System and Stealth Station Surgical Navigation System (Fridley, Minnesota, USA). Ropivacaine was used as a local anesthetic for frame placement. For target locations, measurements were made using CT-scan images fused with previous MR images (both in DICOM format, in axial sections 1.0 mm thick). With the patient under general anesthesia, the stereotactic frame was fixed to the operating table with a Mayfield head holder. Bilateral parasagittal incisions and corresponding 14 mm burr holes (one for each hemisphere) were made in preparation for cell suspension injections. Two different needle tracks through the same burr hole were selected for each side. Target locations were determined by height and length of putaminal nuclei. The lowest Z-coordinates of each track were located in the dorsal putamen and spaced 4mm apart in the X-direction. Each needle track received 1X106 cells in 1 cc of culture medium. To ensure complete cell suspension delivery, injections were carried out slowly for 2 min with reciprocal withdrawal of the delivery needle to avoid both damage to stem cells and brain tissue, as well as to avert reflux or bubble formation. After surgery, patients were kept in a conventional post-operative care unit for 1 h. The day following surgery, MR images were obtained to confirm correct placement of cell suspensions. All patients were discharged 24 h after surgery.