A program for determining the behavior of concrete shear keys under dynamic loading similar to that encountered in nuclear blasts was coupled with a study of the comparative behavior of shear keys under static loading. The testing procedure gave deflection recording for the shear keys, their strength in pure shear, under transverse compression and when dowelled, stresses and strains in the embedded dowels, and the mode of failure of each specimen. From an analysis of the data obtained and a study of the combined direct and transverse stresses involved, important qualitative conclusions were drawn from the common trends in the behavior of keys. The tests proved that plain concrete keys can withstand stresses in pure shear as high as 2000 p.s.i. or more, that imposing transverse compression on them raises the ratio of their shear strength to compressive strength by about 50% in dynamic loading though by only about 5% in static loading, and that the keys exhibit much higher shear strength when subjected to dynamic loads than when stressed by static loads. The test also indicated that the strength and quality of the gravel are probably major factors governing the strength of the keys.