The atomic processes associated with the plastic deformation of commercial-quality sintered iron were investigated. Stress relaxation tests were carried out over the 17–19-kg mm−2 range of initial stress levels at room temperature. The experimental results were analyzed with the deformation kinetics theory discussed in Paper I. The analysis showed that the rate-controlling mechanism is associated with a system of two consecutive energy barriers. At high stress levels only the first barrier is effective. The corresponding activation volume of ∼ 200 b3, measured in these tests, suggested that the Peierls-Nabarro mechanism was rate controlling at this level. It is proposed that the second barrier is either the second half of the ``camel-hump'' Peierls-Nabarro barrier or the resultant of a series of dragging-point barriers controlling the spreading of the double kink.