Before you can start on this study, you will have "screening tests." These tests will help the doctor decide if you are eligible to take part in this study. You will have your complete medical history recorded and a physical exam, including measurement of your vital signs (blood pressure, temperature, breathing rate, and heart rate). You will have a neurological evaluation (a test to evaluate your strength and nerve functioning). You will have blood drawn (about 1 teaspoon or less) and urine collected for routine tests. Women who are able to have children must have a negative urine pregnancy test.