Basic information about nail behaviour, under passive and especially iontophoretic condition, lacks in the literature. Thus, this thesis aims to fill gaps in the nail understanding by studying the potential and feasibility of the application of iontophoresis to human nail. The iontophoretic and passive delivery of Sodium Fluorescein (SF) and Nile Blue Chloride (NBC) were studied, in vitro, in order to determine their pathways as well as their depth and uniformity of penetration into the nail. The permselective properties of the nail were investigated by characterizing the contribution of electroosmosis, using mannitol as a marker, and by studying the flux of two inorganic cations, sodium and lithium, during in vitro experiments. Finally, the feasibility of transungual iontophoresis and the extraction of sodium and chloride ions from the body through the nail plate were performed on a group of human volunteers. Iontophoresis led the fluorescent markers slightly deeper into the nail plate than passive diffusion. The delivery of the bianion and of the cation was not different. Both compounds mainly penetrated the nail via the transcellular pathway. Electroosmosis resulted only in a slight enhancement of the mannitol fluxes compared to passive diffusion and the fluxes presented high variability, especially at pH 7.4 and when the current was applied in the anode-to-cathode direction. The delivery of the two inorganic cations was significantly higher at pH 7.0 than at pH 4.0 and supported that nails hold a negative charge at physiological pH. Ions were easily extractable through the nail plate during in vivo iontophoresis and all volunteers' feedbacks supported iontophoresis as an acceptable technique. This thesis demonstrated the feasibility and potential of in vivo transungual iontophoresis.