Abstract: Tetrandrine showed a wide antiallergic action spectra. For example, it antagonized tracheal contraction induced by the anaphylactie mediators, such as SRS-A, histamine and acetylcholine. In this paper, we report the effects of tetrandrine on ⁴⁵Ca influx in tracheal smooth muscles. Tetrandrine failed to influence the resting ⁴⁵Ca influx in dog and guinea pig tracheal smooth muscles. The rate of inhibition of histamine-stimulated, high K⁺-stimulated and/or-POC opened 5 min ⁴⁵Ca influx in dog tracheal smooth muscles by 60 μg/ml tetrandrine were 11.1% (p>0.05) and 38.3%(p<0.05), respectively; in guinea pig tracheal smooth muscles were 48.7%(p<0.01) and 33.3%(p<0.05). Because tetrandrine blocked histaminestimulated ⁴⁵Ca influx partially and blocked high K⁺-stimulated ⁴⁵Ca influx completely, it was concluded that tetrandrine blocked the potential-operated channel (POC) and receptor-operated channel (ROC) in tracheal smooth muscles with superior blockade of POC. Tetrandrine 60 μg/ml and verapamil 50 μg/ml showed similar potency in the blockade of POC. The calcium channel blockade of tetrandrine could be related to its antagonistic action on tracheal contraction induced by anaphylactic mediators.