The rate of Transcutol® (TC)-water interchange, was studied using whole and stripped hairless rat skin in a modified vertical Franz diffusion cell. The presence of stratum corneum limited the passage of the two solvents, but after stripping of the skin, the rate of TC transfer increased and the water flow rose until the vapour pressure at the skin surface and in the ambient air was similar. The results suggest that TC increased the donor hydration by increasing the outflow of water, with a change in the donor composition. These two opposite fluxes and the alteration of the bulk constitution of the skin and of the donor compartment throughout the experiment, are important factors to be considered for the permeation studies with this solvent.