A method for obtaining the relaxation spectrum of isolated frog skeletal muscle from measurements of phase velocity and attenuation of longitudinal waves, was derived from conventional linear theory of visco-elastic wave propagation. The experimental method for measuring wave velocity and attenuation is described. An approximation method for obtaining the relaxation spectrum from wave velocity alone was developed from theoretical considerations. Experimental results from both the conventional and the approximation methods are presented and compared. Wave propagation measurements appeared to be of value in visco-elastic studies of skeletal muscle, especially when the use of other traditional methods is not practical.