The dynamic emission of screw dislocations from a propagating crack tip has been investigated. The crack velocity and velocity of each dislocation are assumed to be proportional to the third power of the stress intensity factor and the effective stress, respectively. The stress intensity factor for theith dislocation emission is derived according to the spontaneous emission criterion. It is found that the stress intensity factor for dislocation emission is independent of crack mobility but the number of dislocations emitted decreases with increasing crack mobility. The number of emitted dislocations and the size of the plastic zone decrease but the maximum stress intensity factor for dislocation emission increases with increasing initial crack length. The size of the dislocation-free zone increases with increasing initial crack length for steady state. The dislocation–crack system reaches the steady state when the dislocations and crack tip move at the same velocity. ©1997 American Institute of Physics.