Variations of elastic constants and density with strain and the introduction of stresses can significantly affect the propagation velocity of surface acoustic waves. Digital computation using iterative methods is employed to obtain the variations of propagation velocity with strain. It is found that while the individual contributions of the initial stresses, changes in elastic constants, and changes in density with strain can be considerable, their combined effect in some materials may be reduced by mutual cancellation. Computed results forYXquartzYZLiNbO3are compared with experimentally measured values.