Tunneling experiments from superconducting Al base electrodes into both sides of weakly coupled Pb–Cu proximity sandwiches have been performed. The temperature variation and energy of multiple-peaked structure in the normalized tunneling conductance curves compare very well with those calculated using the McMillan tunneling model of the proximity effect, although the calculated curves exhibit more sharply peaked structure than the observed ones. A simple model which takes into consideration the thickness inhomogeneities in the proximity sandwich is proposed in order to account for the sharpness differences.