Striatal dopamine is associated with the processing of rewarded motor tasks. Its involvement in mediating unrewarded tasks is, however, unclear. We used a recently developed PET technique to dynamically measure the rate of displacement of a dopamine receptor ligand raclopride in healthy volunteers performing a finger opposition task. Rapid displacement of the ligand from the posterior putamen and the caudate immediately after the task initiation suggested striatal dopamine release during task performance. Since dopamine release was observed in the striatal areas that are implicated in unrewarded tasks by neuroimaging studies, the results demonstrate that the PET method can be used to extend the findings of conventional neuroimaging techniques, that do not provide information about signal transduction.