This randomized, multicenter, placebo-controlled, double-blind study will evaluate the efficacy and safety of inhaled CVT 301 compared with placebo in PD patients experiencing motor response fluctuations (OFF phenomena) as an outpatient (i.e., at home) and in the clinic.

Inclusion Criteria:

• Idiopathic Parkinson's Disease (PD) diagnosed between the ages of 30 and 80 years;
• Hoehn and Yahr Stage 1-3 in an "on" state;
• Require levodopa-containing medication regimen at least 4 times during the waking day;
• Experience motor fluctuations with a minimum of 2 hours of average daily "off" time per waking day (excluding early morning "off" time) and demonstrate levodopa responsiveness;
• Are on stable PD medication regimen.

Exclusion Criteria:

• Pregnant or lactating females;
• Previous surgery for PD or plan to have stereotactic surgery during the study period;
• History of psychotic symptoms requiring treatment, or suicide ideation or attempt within last year;
• Adequate lung function as measured by spirometry;
• Any significant condition, severe concurrent disease, abnormality or finding that would make patients unsuitable or may compromise patient safety.