Recently, Mead (J. Rheology, 38 (1994) 1797-1827) has shown, for the double reptation model with a monodisperse relaxation function, characterized by a single time constant, how moments for the molecular weight distribution (MWD) can be determined directly from measurements of the linear viscoelastic relaxation modulus. The purpose of this paper is to show that this result is a special case of a more general result which allows linear inner product functionals defined on the MWD, such as its moments, to be determined directly from the measurements. The applicability of this strategy is verified and validated using synthetic data.