This study is designed to determine whether dextromethorphan, a drug commonly found in cough medicine, is beneficial and safe for the treatment of Parkinson's disease and other diseases that might share biochemical abnormalities with Parkinson's disease.

Patients with Parkinson's disease are missing the chemical neurotransmitter dopamine. This occurs as a result of destructive changes in an area of the brain responsible for making dopamine, the basal ganglia. Rhythmical muscular tremors, rigidity of movement, shuffling footsteps, droopy posture, and a mask-like expression on the face characterize Parkinson's disease.

Researchers believe that dextromethorphan may be able to safely modify psychomotor function of patients with Parkinson's Disease.

The ability of the putative excitatory amino acid receptor antagonist, dextromethorphan, to modify psychomotor function safely in patients with neurodegenerative disease will be evaluated using a modified double-blind placebo-controlled design. Therapeutic activity will be rated at various doses by means of standard motor and cognitive performance scales. Safety will be assessed at frequent intervals by clinical observation and laboratory tests.

Parkinson's disease or other neurodegenerative disorders in which excessive stimulation of central glutamatergic pathways is hypothesized.

Patients must be in good general health and have no history or clinical evidence of significant cardiac (including dysrhythmias), pulmonary, gastrointestinal, renal, hepatic, endocrine, hematological or psychiatric disease.

Patient must not evidence any disorder which in the opinion of the investigator imposes an unnecessary risk to the patient or compromises the scientific interpretation of the data.

Individuals of child bearing potential must practice appropriate methods of birth control.