A procedure for evaluating the lateral response of unbraced multistory building frames subjected to a prescribed base motion was developed for use on a digital computer. A Ramberg-Osgood type moment-curvature function was used to describe the inelastic hysteresis behavior of girders, while the columns were assumed to behave elastically. Representative frames of 10, 25, and 40 stories were analyzed. Recorded accelerograms of El Centro 1940, Taft 1952, and Alameda Park, Mexico 1962 earthquakes were used with modified intensities. The results indicate that the shape and intensity of the velocity response spectrum of the earthquakes and the elastic fundamental period of the structures have a marked influence upon their inelastic response. While the elastic behavior of columns is well documented by the results, the hysteresis behavior of girders alone may be a potential source of energy dissipation during a severe earthquake.