Observations of the propagation of plastic band fronts in nonoriented Nylon 6–10 monofilaments have been made as a function of load and temperature, and analyzed in terms of dislocation dynamics. From the shapes and the velocities of the band fronts, dislocation velocities are estimated and found to have a stress dependence similar to that found for nonpolymeric crystalline materials. The measurements yield the following quantities: characteristic drag parameter (3×109dyn/cm2), dislocation density (105/cm2), dislocation multiplication coefficient (20/cm), length of propagating front (10−2cm), and activation energy for the dislocation motion (0.3 eV). The maximum strain required to initiate flow in Nylon is about 40%, independent of the load and strain rate, and in agreement with previous experiments of Milkowitz, and of Williams and Bender. Measurements by Williams and Bender for Nylon 66 have also been analyzed. From the stress dependence of creep incubation times, reasonable values for the mean dislocation velocity in Nylon 66, and the associated activation energy, have been obtained. It is tentatively concluded that the rate of breaking of hydrogen bonds limits dislocation mobility in Nylons 6–10 and 66. The glide system appears to be (100) [001] within the crystallites.