Recently there has been an increase in concern about seismic activity generally and in particular in the Northwest. This interest has been manifested in the upgrading of seismic zones, development of ground motions maps, and updating of the seismic provisions of the building code. The electric transmission grid is by its nature a distributed system. Thus it is reasonable to assume that a transmission tower will be in the vicinity of strong ground motion when a seismic event occurs. Because of this there has been some interest in adding a seismic load case to the traditional load cases already required for the design of electric transmission towers. Structural engineers familiar with the design of electric transmission towers contend that this is not necessary because traditional load cases will control the tower design and produce a safe and reliable structure. It is argued, from a practical point of view, that towers must be the most common structure to be subjected to seismic loads and yet there has been no reported earthquakes that have caused a tower to collapse because of member overstress from ground motion. However, towers have failed due to traditional loads, e.g. wind, ice, and unbalanced conductor tension. The purpose of this study is to determine under what circumstances, if any, a seismic (dynamic) load case controls the size of the primary leg members relative to traditional load cases in an electric transmission tower. The tower leg member, which is the main support for this structure, was chosen because the concern is the collapse of the tower.