A simple experimental setup, consisting of a closed chamber with two electrochemically active walls (the material being studied and one electrochemical pump), was designed to measure the electrochemical permeability of mixed conductors. The basic relations between material properties and measurable parameters are revised. Experiments showed that the quality of sealing is a critical issue to be taken into consideration. Careful analysis of the cell steady-state and transient behaviors (e.g. recovery from reducing to oxidizing conditions) is shown to be quite effective in evaluating the role of physical leaks in the overall experiment.