Our objective was to study the placebo response in Parkinson's disease (PD). We conducted a literature search in which placebo response was measured in all studies of PD from 1969 to April 1996. Strict criteria were defined to include or exclude published reports in our survey. The Parkinson Study Group database for Deprenyl & Tocopherol Antioxidative Therapy of Parkinsonism (DATATOP) was reviewed and placebo "responders" were compared to placebo "nonresponders" by age, race, religion, level of education, duration of PD, and gender. A significant difference between the efficacy of placebo and that of active drug was reported in 61% (22 of 36) of the articles meeting the required criteria; DATATOP analysis showed no statistically significant epidemiologic differences between 140 placebo responders and 58 placebo nonresponders except in PD effect on current job. Although there is clearly a placebo response in PD patients, our review suggests that the variation in placebo response does not correlate with demographic factors such as age, gender, religion, level of education, or duration of PD.