Dislocation slip‐band velocities were measured at 77‐ and 300‐K in well‐ordered Cu3Au single crystals. The results of the 77 and 300 K experiments were very similar: No slip‐band motion is produced at stresses below a critical stress approximately equal to the macroscopic‐yield stress, and bands that were produced during one‐load pulse were never observed to move during subsequent load applications. The slip‐band velocity increases very rapidly in a small stress range above the critical stress.