The transient elastodynamic response of an orthotropic material due to concentrated shear impact loads on the faces of a semi-infinite crack is examined, and the solution for the stress intensity factor history around the crack tip is found. Laplace and Fourier transforms together along with the Wiener-Hopf technique are employed to solve the equations of motion. Even though the problem has characteristic length, it has been shown in previous works that the Wiener-Hopf technique can be applied. The asymptotic expression of stress near the crack tip is analyzed, which leads to the dynamic mode II stress intensity factor. The results are presented for orthotropic materials as well as for an isotropic material. (C) 2001 Elsevier Science Ltd. All rights reserved.