We compared the firing rates and proportion of patterns of oscillatory neurons in the subthalamic nucleus (STN), globus pallidus internus (GPi), and ventrolateral thalamus (VL) in Parkinson disease (PD). Twenty-nine patients with PD who underwent stereotactic neurosurgery were included in the study. Microelectrode recordings in the STN (n = 16), GPi (n = 9), and VL (n = 9) were performed. Power spectral analysis was used to explore neuronal oscillation. Of 76 STN neurons, 39.5% were tremor frequency oscillatory neurons (4-6 Hz, TFB) and 28.9% were beta frequency oscillatory neurons (beta FB); their mean spontaneous firing rate (MSFR) was 44.2 +/- 7.6 Hz (n = 52). Of 62 GPi neurons, 37.1% were TFB oscillatory neurons and 27.4% were beta FB oscillatory neurons; the MSFR was 80.9 +/- 9.6 Hz. Of 69 V L neurons, 65.2% were TFB oscillatory neurons and 11.6% were beta FB oscillatory neurons; the MSFR was 26.7 +/- 5.0 Hz. The increased MSFR of GPi and reduced MSFR of VL oscillatory neurons in parkinsonian patients further support prediction of a pathophysiology model of PD. The high proportion of beta FB oscillatory neurons in the STN and GPi suggests that dopaminergic deficits result in abnormal beta oscillatory synchronization in the basal ganglia in the parkinsonian state. The high proportion of TFB oscillatory neurons in the VL demonstrates that both the basal ganglia and cerebellothalamic circuits are involved in the generation of parkinsonian tremor; the latter circuit might have a more important role in tremor genesis.