The theoretical time response is derived for a pulse reflected from a thin sample of dielectric situated in a coaxial line. The dielectric is assumed to have a distribution of relaxation times. Specific account is taken of the finite rise time of the applied pulse. The equations developed are general and permit the interpretation of measurements without the necessity of transforming to the frequency domain. Explicit equations are developed for the Cole-Davidson and Cole-Cole representations of nonideal dielectrics. Some experimental examples are discussed to assess the utility of the technique.