The industrial demand on good dynamical simulation models is increasing. Since most structures show some form of nonlinear behavior, linear models are not good enough to predict the true dynamical behavior. Hysteresis is a highly nonlinear phenomenon which occurs in for example dampers and mechanical joints. This paper presents a method for parameter estimation on nonlinear systems under harmonic excitation. By using the principle of harmonic balance or multi harmonic balance a theoretical frequency response function of the studied system can be estimated. This frequency response function can, in conjunction with measured nonlinear transfer functions, be used to make parameter estimations of the nonlinearity present in the system. A major benefit using this method is the ability to use arbitrary nonlinear functions. This means that the method can be applied to nonlinear systems with memory, for instance systems with hysteresis effects. The method is applied to both simulated systems and an experimental test rig.