This paper describes an experimental modal synthesis method for determining the noise characteristics of coupled acoustic-structural systems. This method was developed to provide an essential tool for analyzing passenger compartment noise levels. With this method, it is possible to obtain the coupled acoustic-structural parameters directly from experimental measurements of noise and vibration. The resulting modal parameters provide the basis for predicting how structural modifications will affect interior noise characteristics. This paper presents the theory on which the method is based and gives examples of its application to passenger compartment noise analyses.