This paper is concerned with a study of the parameters influencing the seismic design of structures fitted with friction dampers. For the efficient design of such systems, the slip load distribution which minimizes structural response during a major earthquake must be determined for the dampers; this distribution is referred to herein as the optimum slip load distribution. A simple procedure is presented for establishing this basic design parameter. An analogy is first made between a single-storey friction damped structure and a simple nonlinear mechanical system. The response of this system to sinusoidal base excitation is then computed using an existing analytical solution. The solution clearly shows that the optimum slip load of the analogous friction damped structure depends on the amplitude and frequency of the ground motion and is not strictly a structural property. By extension, the optimum slip load distribution of a multistorey friction damped structure will be influenced by the characteristics of the earthquake ground motion anticipated at the construction site. Using this information, numerical sensitivity and parametric studies are performed on multistorey friction damped structures excited by a large number of artificial accelerograms generated from an existing stochastic earthquake model. The results of the study lead to the construction of a design slip load spectrum for the rapid evaluation of the optimum slip load distribution in a multistorey friction damped structure. The spectrum takes into account the properties of the structure and of the ground motion anticipated at the construction site and greatly simplifies the seismic design of this new structural system. Key words: braced frames, brake lining, design, damping, dynamics, earthquakes, energy, friction, slip load spectrum.