The purpose of this study is to evaluate the safety, tolerability, and pharmacokinetics of 4 weeks of continuous infusion with ABBV-951 in adult subjects with Parkinson's Disease (PD).

Inclusion Criteria:

• Subject with a diagnosis of definite idiopathic Parkinson's disease (PD) that is levodopa-responsive according to the United Kingdom Parkinson's Disease Society Brain Bank Criteria.
• Subject must be taking an optimized and stable regimen of oral medications for PD, which has remained stable and unchanged for at least 30 days before enrollment in this study.
• Subject is judged inadequately controlled on current therapy in the opinion of the Investigator and must experience a minimum of 2.5 hours of "off" time per day prior to Enrollment.
• Subjects with a MMSE score greater than or equal to 24 and considered by the Investigator to not have dementia.

Exclusion Criteria:

• Subjects with clinically significant electrocardiogram (ECG) values.
• History of significant skin conditions or disorders that in the Investigator's opinion would interfere with the infusion of the study drug or could interfere with study assessments.
• Receipt of an investigational product within at least 6 weeks prior to study drug administration.
• Subjects with moderate to severe kidney disease.
• Consideration by the investigator for any reason that the subject is an unsuitable candidate to receive ABBV-951.
• Patient/caregiver that cannot demonstrate proper use of the devices (drug pump and wearable device) will not be allowed to participate.