The effects of subthalamic nucleus (STN) stimulation on the pedunculopontine nucleus area (PPNR) evoked activities were examined in two patients with Parkinson's disease. The patients had previously undergone bilateral STN deep brain stimulation (DBS) and subsequently received unilateral DBS electrodes in the PPNR. Evoked potentials were recorded from the local field potentials (LFP) from the PPNR with STN stimulation at different frequencies and bipolar contacts. Ipsilateral and contralateral short latency (<2ms) PPNR responses were evoked from left but not from right STN stimulation. In both patients, STN stimulation evoked contralateral PPNR responses at medium latencies between 41 and 45ms. Cortical evoked potentials to single pulse STN stimulation were observed at latencies between 18 and 27ms. These results demonstrate a functional connection between the STN and the PPNR. It likely involves direct projections between the STN and PPNR or polysynaptic pathways with thalamic or cortical relays.