The usefulness of optical measurements in the 1 – 20μ region in the understanding of electron‐phonon coupling in transition metals is discussed. There are many possible barriers in the way of exact simple relations of optical constants to superconductivity, and some of these are described. In many transition metals the relaxation rate has the form α + βω 2 . Possible origins of the term are given, of which the two most interesting are the rapid variation of parameters near the Fermi energy, and electron‐electron collisions. It is shown that the measured Baber resistivity term in palladium is in qualitative agreement with this interpretation of the βω2 optical relaxation rate in palladium.