The electrochemical behavior of nanoporous and smooth carbon electrodes was investigated in a phosphate-buffered saline solution. The interfacial properties were characterized by electrochemical impedance spectroscopy. The influence of charging/discharging rate on the capacitive behavior was investigated by cyclic voltammetry between -3 and 1 V at fast sweep rates. The transient processes taking place at the electrode upon stimulation pulse were also studied by using a pulse generator. For the nanoporous electrode at sufficiently high sweep rates, the charge-transfer characteristics change from capacitive to resistive, due to voltage drop down the pores. Only a small part of total available capacitance of the porous electrode can be utilized at high charging/discharging rates. This is probably the reason for the observed relationship between pacing impedance and geometric electrode surface area. When subjected to stimulation pulses, compared to the smooth electrode, the nanoporous electrode delivers more charge due to lower pacing impedance. At high pulse potentials, some faradaic reaction seems to occur, which is more pronounced on the smooth electrode. (c) 2005 The Electrochemical Society.