The dynamic stress field near a propagating crack tip is usually characterized in terms of one parameter, namely, the dynamic stress intensity factor. While analytically this is an exact representation at the crack tip itself, under transient conditions, the domain of dominance of the stress intensity factor varies as discussed by Ma and Freund (1986). In this paper, we present experimental results which show that while the stress intensity factor may dominate the near tip stress field under transient conditions as long as the crack velocity is small, it may not be dominant over an appreciable region under other transient conditions of crack tip motion, thus making it difficult to determine this quantity experimentally.