The safety and initial efficacy of the unilateral intralenticular infusion of recombinant-methionyl human glial cell line-derived neurotrophic factor (r-metHuGDNF) will be compared with the contralateral intralenticular infusion of a placebo solution, both continuously administered using chronically implanted catheters and pumps in up to 10 patients with progressive supranuclear palsy. Safety will be evaluated by analyzing implant-, post-implant-, and treatment-emergent adverse events, clinical laboratory test results, and disease status. Efficacy will be studied by comparing left and right sided neurologic function using validated clinical scales as well as by putative surrogate biochemical and radiographic measures.