An investigation has been performed on the plastic behaviour of a mild steel within the region of dynamic strain ageing. For this purpose tension tests have been performed on annealed XC18 steel within a range of temperatures, from 305-776 K, and a range of strain rates, from 1.0 x 10(-4) - 1.85 x 10(-1)s(-1). An analysis of experimental results is presented using a model for plastic deformation based on dislocation multiplications.