Iontophoresis, which enhances the rate of charged drugs through a membrane by applying an electric current, is a novel promising technique for a drug delivery system. The authors used iontophoresis to enhance the skin permeability of drugs in transdermal delivery. In vitro permeation experiments across a piece of excised hairless mouse skin were made with/without electric field application. A model drug, benzoic acid (BA, MW=122), did not passively penetrate through the intact hairless mouse skin at pH=7.4 (almost completely ionized); however, it could appreciably permeate through the skin when an electric current density of 3.0 A/m(2) was applied. The permeation flux of BA through the skin was linearly changed with the electric current density, which makes it possible to control drug concentration in the blood periodically. The permeation flux of dexamethasone sodium m-sulfobenzoate (MW=599), which is larger than BA, was also enhanced by applying iontophoresis. Computer simulation was performed for iontophoresis experiments using transport parameters determined from passive diffusion experiments. Experimental findings under iontophoresis were well correlated by the results of computer simulation, which may be useful for designing an optimal administrating schedule for a specific drug.