Six methods for calculating the natural frequency and mode shapes of cross-stiffened plating were examined particularly for their application to plating with a large number of small closely spaced stiffeners in one direction supported by a few deep girders in the other. The best method was able to predict at least 1 6 frequencies (all that were measured) of a model with a maximum error of less than 15 percent when proper boundary conditions were used. The maximum error in nodal-line locations for the best method was 5.2 percent of the span