In this work, an electrochemical method used for the determination of solid-liquid mass transfer coefficients has been applied to the measurement of the Sherwood number for the stationary diffusional mass transfer between a porous material and a stationary liquid in the pores. Such a minimum Sherwood number was determined for sintered metals and for fixed beds of spherical grains. The theoretical aspects are based on the analogy of the problem with competition between molecular diffusion and heterogeneous chemical reaction in a porous catalyst.