In this Letter a method is described for computing the response of a linear three-dimensional classical model of the cochlea. The method can be applied when the geometry of the model lends itself to separation of variables, for instance, when the model has the shape of a homogeneous rectangular block or box. The method is an improvement over previously published computation methods, because it handles forward and retrograde traveling waves symmetrically, and it can be used for forward as well as inverse solutions. Furthermore, the method can be extended to a time-domain solution.