This paper discusses the validity of the pulsed-neutron experiments frequently used for checking core-shutdown calculations. The analysis of the experimental methods is based on energy-dependent diffusion theory, since this, in its few-group form, is the usual core-design model. It is shown that the comparison of experimental and theoretical values of the fundamental-mode prompt decay constant is a valid check, but the Garelis and Russell method is subject to severe limitations. We show that certain assumptions must be made to deduce the Garelis and Russell equation and recommend that the experimenter check the extent to which these assumptions are violated before he attempts to use the Garelis and Russell method.