Abstract: Tetrandrine was shown to significantly inhibit the contraction of guinea pig tracheal or lung strips induced by SRS-A 100 U/ml in vitro. It was also found to inhibit the contractile effect on human bronchial or lung strips induced by SRS-A U/ml in vitro.Tetrandrine 25 mg/kg given intravenously prior to SRS-A antagonized the augmentation of respiratory airflow by SRS-A.The SRS-A induced asthmatic attack of guinea pig was also alleviated by tetrandrine. The anti-SRS-A effect of tetrandrine was reduced when the extracellular Ca⁺⁺ level was elevated and vice versa.