Excessive synchronisation of basal ganglia activity at frequencies <30Hz is a hallmark of the parkinsonian state, and may contribute to bradykinesia. Accordingly, we electrically stimulated chronically implanted subthalamic macroelectrodes in 10 Parkinson's disease patients, after overnight withdrawal of anti-parkinsonian medication. We compared the effects of stimulation at 0, 5, 10, 15, 20, 25, 30, and ca. 130Hz by measuring kinesia time (KT) in a tapping task. Although the effects of direct stimulation were small, frequency–response curves demonstrated local peaks at 5–10Hz and at 20–25Hz, superimposed upon an overall tendency for KT to reduce with increasing stimulation frequency. This is consistent with the hypothesis that spontaneous activities in these bands might promote bradykinesia.