The serious serious sequelae of sprains of the knee and ankle makes it imperative for the therapist to have an early and precise diagnosis. The authors propose a means of exploring these joints with the aid of a simple set up. This new technology allows the radiologist, secure from direct or indirect radiation, to carry out a standardized examination of the joint, usually unilaterally, and to make his interpretation more easily and more precisely. This method of x-raying in the stress position has its major indication in emergencies, but is equally useful in non emergencies, accomplishing a veritable over-all evaluation of the joint: varus, valgus, preternatural anterior and posterior sliding motion. The interpretation, based on direct reading of the films, differentiates the normal condition from physiological relaxation and mild and severe sprains. Naturally this method is to be used only after taking standard routine views to rule out any fractures.