The effects of acupuncture stimulation to the sacral segment on the electroencephalogram (EEG) and activity of the cholinergic neurons in the laterodorsal tegmental nucleus (LDT) were examined in urethane-anesthetized rats. When EEG was small amplitude and higher frequency , the stimulation to the sacral segment induced large amplitude and slow EEG with latencies ranged from 45 sec to 12 min, and durations from 48 sec to 56 min. The stimulus induced EEG is composed of significant increase in delta power and significant decrease in theta and beta powers. Firing rate of the cholinergic LDT neurons significantly decreased from 2.9±1.5 Hz to 1.1±0.8 Hz after the stimulus (n=l2, p<0.05). The decrease of neuronal activity always preceded to the start of large and slow EEG, while the increase of the activity always preceded to the change of EEG from large slow wave to small faster wave. These results suggest that the acupuncture stimulation to the sacral segment changes the state of the animals from light anesthesia to deep anesthesia, and that the change is mediated by the suppression of the cholinergic neurons in the LDT.