The earthquake responses of a twenty-story nonlinear structural frame representative of a modern high-rise building were calculated. The structure was modeled by a two-dimensional frame with girders and columns having bilinear bending moment-end rotation hysteretic characteristics. In addition to hysteretic damping, viscous damping mechanisms were assumed. The earthquakes used were the El Centro (N-S) earthquake of May 18, 1940 and several pseudo-earthquakes having statistics similar to those of previously recorded earthquakes. Time history plots for displacements, bending moments, joint rotations, etc., at several stations in the structure are presented. A displacement envelope and a plot of the ductility factors, which measure the amount of yielding incurred, are also given. It was possible to identify certain behavior characteristics of the structural responses which appeared to be determined more by the properties of the structure than by the earthquake. For the series of pseudo-earthquakes used, a large range was found in the maximum values of the responses of the yielding structure. For example, the spread between extremum values of the maximum absolute displacements was 50 per cent of the arithmetic mean value. Statistics of the magnitudes of the displacements and ductility factors were compared with three common measurements of the strength of earthquake accelerograms. It was found that none of these three measurements correlated well with the trend of the maximum responses.