The influences of Ca²⁺-antagonists, verapamil and Mn²⁺, upon the spontaneous electrical activity and contractions were studied in guinea-pig taenia coli. Spontaneous contractions were recorded with force transducer, and spike action potentials were measured extracellularly by use of suction electrode. All experiments were performed in tris-buffered Tyrode solution Which was aerated With 100% O₂ and kept at 35℃. The results obtained were as follows : 1) Verapamil suppressed the frequency and amplitude of spontaneous contractions dose dependently, and blocked completely mechanical responses at the concentration of 1 mg/1. 2) The frequency of bursts of spike discharge(bursts frequency) and the number of spikes in a burst(spikes frequency) were reduced in a dose¡¤dependent manner within the concentration range of 10^-5 to 10^-3g/l, and bursts frequency was affected more readily at a low concentration of 10^-5g/l verapamil. 3) The verapamil_induced suppression of spontaneous contractions in the Tyrode solution containing 1 mM Ca²⁺ was completely antagonized by the addition of extra Ca²⁺ to the Tyrode solution (2 m MCa²⁺). 4) Mn²⁺ suppressed the amplitude of spontaneous contractions, whereas Mn²⁺ accelerated the frequency dose-dependently within the range of low concentrations(10^-7 to 10^-4 M Mn²⁺). 5) The bursts frequency determining frequency of spontaneous contractions was increased in a dose-dependent manner, whereas the spikes frequency known to determine the contractions amplitude was reduced within the range of low concentrations. At a high concentration of 1 mM Mn²⁺, however, all spontaneous contractile responses were blocked simultaneously with the disapperance of electrical activity. 6) The frequency and amplitude of spontaneous contractions altered by Mn²⁺ in 1mM Ca²⁺ Tyrode were increased by extra Ca²⁺(2mM).