Stannous chloride (SnCl2) facilitates the calcium (Ca) entry into the frog motor nerve terminals. To compare the mode of action of SnCl2 on the Ca channels in the mouse with that in the frog, we investigated the effects of SnCl2 on the inward Ca current at the nerve terminals. SnCl2 (0.1 mM) did not change the second positive component of the action potential (an outward potassium (K) current) at the terminal part of the nerve terminal. SnCl2 (0.1 mM) increased the amplitude of the prolonged negative or positive deflection (an inward Ca current) evoked by treatment with 1 mM tetraethylammonium and 0.1 mM 3,4-diaminopyridine at the terminal or preterminal part of the nerve terminal, respectively. This augmenting effect of SnCl2 was inhibited by cumulative addition of Ca channel blockers, i.e., 0.1 mM CdCl2, 5 mM NiCl2, 5 mM CoCl2, 5 mM MnCl2, or 10 mM MgCl2. From the results obtained, it has been confirmed that SnCl2 facilitates the transmitter release by enhancing the Ca influx at the nerve terminals but not by blocking the K channels and that the mode of action of SnCl2 in the mouse is identical with that in the frog.