In this paper, steady-state, dynamic crack growth has been analysed under mode I plane stress, small scale yielding conditions using a finite element procedure. A Perzyna type, overstress viscoplastic constitutive equation has been employed in this analysis. A fracture criterion based on critical plastic strain has been imposed to obtain (theoretically) the variation of dynamic fracture toughness with crack speed, when crack propagation occurs in a ductile mode. The viscoplastic work rate is converted into heat input and the temperature rise distribution is determined by solving the governing conduction/convection equation, also by a finite element method. The effect of rate sensitivity and crack velocity on the fracture toughness and the temperature distribution have been clearly brought out in this study. © 1991.