Publication costs assisted by the National Science FoundationAn algorithm for computer simulation of transient concentration profiles and both transient and ac electrical properties of conducting membranes has been developed and described. Applications include transport by several ions with different mobilities and valences in permselective membranes, totally blocked cells, and finite galvanic cells. The algorithm is based on the Nernst-Planck system of equations coupled with Poisson's equation, introduced via the displacement current; therefore, electroneutrality is not assumed and migration effects are included automatically. Simulations of transient and steady-state properties as well as ac impedances are compared with solutions obtained analytically. Conventional linearization of field equations is not required to obtain transient responses. However, conversion from time to frequency using the Fourier transform to obtain impedances is theoretically limited to dimensionless currents and voltages less than unity. We have demonstrated versatility of the algorithm by simulating a case of biological interest-the inductive behavior of the squid giant axon.