A procedure based on the use of the describing function is presented to identify the parameters of a nonlinear system incorporating cubic stiffness elements. The procedure uses frequency response data at resonance, obtained from different forcing levels, to identify both the linear and nonlinear parameters of the system. Under noisy conditions an effective variance method of solution is used which shows less sensitivity to noise than the classical weighted least squares method. Furthermore, the method gives encouraging results when used as a means for locating cubic elements situated within the system. Simulated experiments and results are included to illustrate the feasibility of the method under noisy measurement conditions.