 2. Subject-rated dyskinesia severity: Dyskinesia severity will be rated by the patient using several validated methods Lang-Fahn Activities of Daily Living Dyskinesia scale, Clinical Global Impression, Unified Parkinsons Disease Rating Scale, and home dyskinesia diaries. Rating scales will be completed at the time of each levodopa challenge and at 2-week intervals. Dyskinesia diaries will be completed for 3 days prior to each levodopa challenge. 