The effect of state of stress on the shear wave velocity and shear modulus of a dry sand was examined. Testing was performed in a large-scale triaxial device in which cubic soil samples measuring 7 ft on a side were loaded in isotropic, biaxial, and triaxial states of stress. Stiffness of the sand skeleton was evaluated by propagating shear waves along each principal stress axis of the sample over ranges in pressure from 10 to 40 psi. All testing was performed at low-amplitude strains (less than 0. 001 percent) and at wave frequencies less than 3000 Hz. Shear wave velocity was found to depend about equally on the principal stresses in the directions of wave propagation and particle motion and was determined to be relatively independent of the third principal stress.