Abstract. A similarity transformation is used to reduce the system of second-order equations, governing elastodynamic plane problems in an orthotropic medium, to a first-order elliptic system of the Cauchy-Riemann type. A complex variable notation is then introduced to derive in a straightforward way the solution of two noticeable elastodynamic crack problems.1. Introduction. The problem of determining the stress field induced by a steadily propagating crack in a two-dimensional elastic medium is of primary interest in fracture mechanics. A great many results have been obtained for isotropic materials, and dutiful mention is made to the more significant analytical studies.Yoffe [1] discussed the plane problem of a crack of constant length moving with constant speed in an isotropic medium stressed at infinity. The same problem was solved later by Radok [2] who used a complex variable method.Craggs [3] considered the shape of a semi-infinite crack loaded over a segment of its edges. In solving the related boundary value problem, he used Cauchy's integral representation which, however, does not permit one to determine analytically the singular terms of the solution.