Effects of l-tetrahydroberberine-d-camphor sulfonate (THB-CS) on spontaneous EEG, arousal response and recruiting response were investigated in rabbits and rats in comparison with those of chlorpromazine. The spontaneous EEG recorded from the motor cortex and hippocampus showed a prominent resting pattern 3-5 min after intravenous administration of THB-CS in doses more than 0.01 mg/kg in rabbits and 30 min after oral administration of the drug in doses more than 1 mg/kg in rats. These effects lasted for 30-60 min after i.v. administration and 60-90 min after oral administration; however, the effects were not proportional to the doses up to 8 mg/kg (i.v.) and 12.5 mg/kg (p.o.). The abnormal characteristics of the EEG pattern such as seizure pattern and flattening were not observed. Chlorpromazine also produced the resting pattern in doses of 2 mg/kg (i.v.) in rabbits and 1 mg/kg (p.o.) in rats. THB-CS and chlorpromazine produced a slight elevation of threshold for the EEG arousal response elicited by high frequency stimulation of the midbrain reticular formation, but did not alter the recruiting response elicited by low frequency stimulation of the centromedian nucleus of the thalamus. These results suggest that the effects of THB-CS resemble those of chlorpromazine, but are different from those of barbiturates.