A method is developed for determining the dynamic force-deflection relation of a one-degree of freedom hysteretic structure from the steady-state response to sinusoidal excitation. The data needed are the resonant frequency and the equivalent viscous damping factor, as defined in the paper, as functions of the amplitude of steady-state response. The method is applicable to oscillators of the Masing type, a classification which includes the more common models of yielding behavior (e.g., elasto-plastic, bilinear hysteretic). Examples of the application of the method to mathematical models of hysteretic structures and to dynamic test data are given.