Design: Patients and healthy volunteers enter this Protocol after undergoing clinical laboratory evaluation under NIH Clinical Protocol 03-N-0004, to confirm the diagnosis, identify NOH, and provide data related to central or peripheral NE production. Each subject serves as his or her own control. Subjects are tested after taking a single oral dose of 400 mg of L-DOPS in a randomized crossover design study of three treatment conditions L-DOPS alone, L-DOPS after carbidopa (200 mg), and L-DOPS after entacapone (200 mg). Healthy volunteers have CSF drawn by lumbar puncture under fluoroscopic guidance about 3 hours after administration of each drug combination.