\ The suitability of three animal skin species as the model for iontophoresis study was discussed based on the current density measurement, compared with the electrical properties of the human epidermal membrane (HEM) in vitro. The hydration during 48 h period significantly and continuously decreased the animal skin resistance and had much smaller influence on the HEM. The relationship between the pulse voltage and the current across these skin models was similar to those of HEM in different hydration status, but there were some variations in the extent due to the various sensitivities. The profiles could be simulated by the equation of V=(4ART/F) sinh-1 (BI). The parameters A reflected the sensitivity of the skin species to the electrical field. The hairless mouse skin and hairless guinea pig skin were more sensitive than the HEM, the sensitivity of the hairless rat skin was the lowest among the skin species. The results were further proved by the tests of long period voltage regimens, but it was found that significant alteration of the skin resistance occurred in the very short time as the electrical field was set up or discontinued.
