This paper presents the results of experiments in which two thinwalled tubes of commercially pure aluminium in the annealed condition were loaded in combined tension and torsion in the plastic region at elevated temperatures. In the first test prestressing was in torsion but of a cyclic nature. In the other test prestressing included a path reversal in tension. It is shown that the hardening law introduced previously [3] is such that prestressing towards the origin of the stress space produces an increase in the width of the yield curve in the prestressing direction. It is also shown that a locus of zero deformation of yield surfaces can be postulated.