Metal Building Systems (MBS) make up a substantial portion of non- residential, low-rise construction in the U.S. Given their wide spread use, it is desirable to understand their performance during a seismic event. Previous pseudo- static, cyclic testing indicates an absence of ductility in these systems. This lack of ductility arises from the inherent design concepts behind using web-tapered frames with no flange or web compactness limits, causing buckling limit states to govern the strength of the frames. In light of the lack of ductility, it is obvious that the current practice of designing MBS moment frames as Ordinary Moment Frame (OMF) systems, with R=3.5, is inappropriate. Also, simple analytical studies suggest that MBS supporting large masses, such as concrete or masonry exterior cladding or interior mezzanines, may be particularly vulnerable to the lack of ductility. For these reasons, it is desirable to develop a safe, economic, and reliable design procedure for MBS. Earthquake simulation testing of MBS has been performed to provide test data to start this development. Three full-scale MBS specimens have been tested on the NEES/UCSD Large High Performance Outdoor Shake Table. Specimen 1 consisted of a single story MBS frame with metal side wall panels to represent the majority of MBS buildings. Specimen 2 was similar to the first, except with heavy concrete sidewall panels. Specimen 3 consisted of a MBS frame built with compact flanges, a mezzanine attached to one sidewall, and a concrete wall attached to the other. Results from each battery of tests will be presented in this paper.