Abstract: Verapamil (Ver 0.25% aerosol) was shown to inhibit asthma induced by histamine and acetylcholine in guinea pig. Ver (10^-3M) produced a slight but statistically significant inhibitory effect on the release of histamine from the lung of ovalbumin sensitized guinea pig by the antigen challenge. When Ver (0.25%) and isoproterenol (ISO 0.005% aerosol) were used together, the antagonistic effect of ISO on chemical asthma of guinea pig was markedly increased. Ver (10^-4M) also significantly increased suppression of anaphylactic histamine release by ISO (the inhibitive rate of 10^-8M ISO was increased from 39.3% to 50.0%, and that of 10^-7M ISO from 49.0% to 65.0%). The relaxant effect of ISO on the guinea pig tracheal smooth muscle was markedly increased by 5×10^-5M Ver. The pD₂ values of ISO had an increase of 0.61±0.25. In Ca²⁺-free, high K⁺ depolarized guinea pig trachea, ISO (10^-7M) was not capable of depressing contraction produced by extracellular Ca²⁺. The pD₂ values of ISO were 7.77±0.11 (n=10)and 7.99±0.14 (n=10) in the Ca²⁺-free and 10mM Ca²⁺ medium, respectively (p> 0.05). ISO (10^-7M) showed no influence on the contraction produced by high K⁺, which caused the release of intracellular calcium. The relaxant effect of ISO was abolished by the addition of 2mM EDTA to chelate the available intracellular free calcium ions. It was concluded that the relaxant effect of ISO on the guinea pig tracheal smooth muscle was unrelated to extracellular calcium and release of intracellular calcium, but was related to available intracellular free calcium ions. So, ISO was different from Ver in their effect on calcium transport system. All these results served as an experimental basis of using ISO in combination with Ver for asthma therapy.