The objective of this study was to compare basal ganglia activation in patients with Parkinson's disease to that of healthy controls, using functional MRI (fMRI). Six mildly-affected patients, off antiparkinsonian medications for at least 12h, and seven age-matched controls performed a unilateral motor switching task during fMRI data acquisition. Clear differences in basal ganglia activation were seen, with control subjects showing greater activation during both the left and right movement sessions. We observed activation of right sided basal ganglia structures in both groups, particularly with right sided movements, with caudate activation noted most frequently. This observation is consistent with right caudate involvement in the learning of new tasks and in association with externally paced movements.