Papaverine, benactyzine and Aspaminol were found to induce strong contractions of guinea pig ileal longitudinal muscle in a medium containing 3.2 mM of Ca2+. The contractile actions of papaverine, benactyzine and Aspaminol were potentiated with increase in Ca2+. The contractile actions of papaverine, benactyzine and action of papaverine was completely blocked by Mn2+, which by itself caused a contraction of the longitudinal muscle. The maximal contraction by papaverine was obtained at the concentration of more than 10(-5) M, WHILE BOTH BENACTYZINE AND Aspaminol induced the maximal contractions at the concentration of 3 X 10(-4) M. During and after the contraction by papaverine, contractile responses to benactyzine and Aspaminol were not observed. Changes in the intracellular level of cyclic GMP after exposure of the longitudinal muscle to papaverine, benactyzine or Aspaminol did not occur. These results suggest that papaverine, benactyzine Aspaminol may induce contractions of the ileal longitudinal muscle through a similar mechanism of action. A likely assumption is that these drugs move intracellular bound Ca2+ to the contractile protein of the muscle.