A consecutive series of 30 cases of Parkinsonism were examined in this study. A prove with five silver ring electrodes at 5 mm distance from the tip was inserted into the ventrolateral nucleus of the thalamus stereotaxically. Spontaneous thalamic activities of the patients were recorded and analyzed by Walter type analyzer with electrical filters into five bands, i.e. 2-4 c/s, delta band; 4-8 c/s, theta band; 8-13 c/s, alpha band; 13-20 c/s, beta I band; and 20-30 c/s, beta Ⅱ band. EEG from parieto-occipital region were also recorded and analyzed simultaneously. Frequency power spectrum of the thalamus showed generally higher theta and delta band activities in both bipolar and monopolar records. In the patients with predominant tremor of the limbs it showed considerable high delta band and marked low alpha band activities, which were clearly differentiated from that of other type of Parkinsonism. This was characteristic in the bipolar record from the thalamus. Duration time of waxing and waning phenomenon of alpha band activity ranged from 0.9 to 2.0 seconds with average 1.2 seconds in the thalamus, but longer duration up to 5 seconds in the scalp lead. Frequencies of alpha activities were noted mostly from 8.5 to 10.5 c/s. in EEG, but 8.5 to 11.5 c/s. in the thalamic lead. The patients with higher frequencies of alpha activities were closely corresponded to a good candidate for surgery in the thalamic bipolar lead, but not in thalamic monopolar lead or scalp EEG. On the other hand, a poor candidate for surgery had higher delta and theta activities in the frequency power spectra and slowing of frequencies of alpha activities in the thalamic bipolar lead. The scalp EEG findings were not specific, but thalamic activities were most closely related to the progress of symptoms, particularly tremor, rigidity and bradykinetic situation of a Parkinsonian patient.