Microelectrode arrays intended for transmural cardiac recording applications with recording sites of silver chloride and platinum black were prepared using integrated-circuit (IC) techniques. The optimum method of preparing each recording medium is described along with the best way to store the electrodes before use. The silver chloride electrodes should be stored in 0.9% saline for 48 h prior to use for minimal impedance magnitudes. The platinized electrodes were subjected to three different storage environments: air, nitrogen, and 0.9% saline. Impedance measurements involving magnitude and phase were used to compare the effects of each of these storage environments. Platinum black has shown stability in its electrical characteristics in each of the three storage environments tested.