As predictive testing for Parkinson's disease (PD) becomes available, it will be important to understand in whom such testing will be used. To address this issue, we conducted a mail survey of 138 first-degree relatives of PD patients. In the absence of treatment, 60% reported that they would either "definitely" or "probably" be interested in predictive testing. In the setting of a clinical trial, this number increased to 71% (p=0.04) and when neuroprotective therapy is available, interest increased to 90% (p<0.001). Interest in predictive testing for PD is moderate in the absence of effective therapy, and goes up significantly when both clinical trial participation and neuroprotective therapy are offered.