Interactions between modes in nonlinear structures can lead to situations where, for the same excitation, different responses may be observed. The observed response will be a function of the system, of the excitation, of initial conditions, and of the effects of small perturbations to the system. Some responses may be observed more often than others. When the more rarely observed responses are perceived as problem situations, it is often frustrating to demonstrate that the problem exists, because it is difficult to control the test sufficiently to repeatedly observe the behavior. Analysis of system models can be used to identify under what conditions these responses may occur, and indicate how the region where such responses are possible may be approached. In real systems, the model structure for the system has to be identified, which may be an affirmation of a theoretical model structure, and the parameters of these models estimated. Described in the presentation are the results of using a system identification technique to construct models relating the excitation to the response of two interacting modes in a thin plate under tension.