This paper develops a method for locating structural damage using experimental broadband data. The method uses measured frequency response functions to obtain displacement as a function of frequency. The displacement functions are processed to yield a damage index, displayed on a plot of position versus frequency. The method can be applied when there is no a priori knowledge about the undamaged structure. The method can be automated. This paper details the theory of the broadband method, and the results of an experimental demonstration in which a steel beam was damaged with a narrow slot. It is shown that this method is highly sensitive, and can locate a very small amount of damage. For example, the slot was correctly located when there was only a 0.8% reduction in thickness. Traditionally, damage causes a change in natural frequencies, but at this small level of damage the frequency changes were within experimental error.