An analysis is presented of the impact process occuring when a hard ball strikes the surface of a large metal specimen. It is shown that the results of dynamic indentation tests can be interpreted to provide a measure of the yield stress of the metal over a range of strains taking into account the influence of strain-rate. Experiments are described in which steel balls are allowed to drop onto specimens of lead, steel and aluminum. In each test the velocities of impact and rebound are measured as well as the diameter of the indentation remaining in the metal specimen and the time of contact between specimen and indenter. These experimental results are used in conjunction with the analysis to provide for each metal a dynamic stress-strain curve which is then compared to results of a simple compression test performed under impact conditions. For all metals the best agreement occurs if the simple compression tests are performed at a strain-rate of 1,500 sec(-1). The analysis also provides a model of the indentation process which furnishes quite accurate predictions of the size of the permanent indentation, the time of contact during impact and the coefficient of restitution.