Abstract For many years the relationship between the velocity of deformation and the resulting stress has been occupying the attention of several investigators. In general, the tests have been made under uniform tensile- or compressive-stress conditions. It was with the object of investigating this relationship when under pure shear conditions that the work outlined in this paper was undertaken. Except for a few isolated cases, there are no results available with which comparisons may be made, but it appears from the tests made that the influence of the rate of deformation upon the ultimate strength is considerable. The results indicate that in all likelihood the same relationship that has been found to exist for conditions of direct stress will hold for conditions of pure shear. That is, the equation proposed by Ludwik, σ = σ1 + C log (v/v1), for the case of pure tension has been found to prove satisfactory for pure shear. Only one metal (lead) has been tested, but the results so found may be taken as representative of those materials with a low melting point. Further, in all probability the behavior of steels, when subjected to constant rates of shear and when maintained at some relatively high temperature, will lead to similar results.