Biologic tissue has been modelled as a viscoelastic Voigt body for the propagation of ultrasound. The tissues considered are man and cow livers, dog myocardial tissue, and cow tongue. Published ultrasonic attenuation data have been correlated, on the basis of a single relaxation frequency, in the frequency range of 0.8–10 MHz. From this correlation, approximate values of elastic moduli have been estimated. The value of the shear modulus appears to be negligible compared to that of the bulk modulus. The value of the relaxation bulk modulus depends upon the type of tissue and its orientation to the sonic beam. The velocity dispersion in tissue has been estimated from the values of bulk moduli.