Kinetics of slow current carried by sodium ions through the potential-dependent calcium channels provided that EDTA is introduced into Ca-free external solution was studied in experiments on isolated internally dialyzed neurons of the mollusc Helix pomatia. Activation kinetics of this current was similar to that of initial calcium current. It can be described using the square power of the activation variable m in the Hodgkin-Huxley equations. Kinetics of decay (inactivation) of the induced sodium current is biexponential during prolonged depolarization of the membrane. On this basis it is suggested that the decay of the sodium current results from two independent processes: voltage-dependent inactivation to some steady-state level hoo with time constant tauh approximately 1 s and a decrease of the current due to accumulation of Na+ ions inside the cell and, consequently, to a change in electrochemical potential for Na+ ions (tau c approximately 10 s). It is concluded that modification of calcium channels resulting in ability for passing sodium ions does not affect gating mechanisms which open or close the channels.