First- and second-order asymptotic solutions are given for the problem of a Mode I crack rapidly propagating in an elastic-viscoplastic solid. Results are obtained for the order of the crack-tip singularity, the angular position at which unloading occurs, and the angular variations of stresses and velocities. It is shown that the eigenvalue, which determines the order of stress singularity, relates only to the viscoplastic parameters but is independent of the crack speed, the boundary condition, and the loading conditions. In addition, it is shown that crack speed has a limiting value, which is the Rayleigh wave speed of the medium and is independent of the inelastic properties of the material. Beyond this limiting speed only a trivial solution exists. Numerical computations reveal that no re-loading zone is observed.