Reactor period-reactivity relations and open-loop transfer functions may be determined directly by numerical integration of “rod-drop” neutron decay data without analysis into delayed neutron period and abundance values. Period-reactivity relations obtained by this method for two critical assemblies with and without beryllium in the core and reflector are compared with corresponding results calculated from the “in-hour” equation. Results of the application of the rod-drop experiment to the determination of the open-loop reactor transfer function are given for the beryllium-moderated assembly.