Abstract: In rabbits, 1-Tetrahydropalmatine (1-THP) 10,20 or 30 mg/kg, ⅳ, induced loss of righting reflex. The dose-effect relation ship appeared to be linear which was shifted to the left when dihydroetorphine (DHE) 1 μg/kg was given ⅳ in combination with 1-THP. The EEG changed gradually from low voltage rapid wave to high voltage slow wave. In mice, 1-THP (10 mg/kg, ip) and DHE(2 μg/kg, ip) elevated the pain threshold (hot plate method measured at the 10 th min) by 135±35% ((?)±SD) and 40±10% (P<0.01 respectively. However, when the two drugs were given in combination, the pain threshold increased by 339±20%. These results suggest that their actions on CNS are synergistic.The decrease of heart rate in rabbits, following DHE could be antagonized by B-7601. DHE was shown to inhibit respiration and this action was antagonized to some extent by 1-THP.The combined use of DHE(1 μg/kg), B-7601 (0.5mg/kg), a new muscarinic antagonist, L-THP (20 mg/kg) and diazepam (2 mg/kg) by the ⅳ route induced immediate general anesthesia and disappearance of electromyogram in dogs. The duration of the loss of righting reflex was 172±44 min. Thus, an adequate anesthetic state for abdominal operation could be attained.