Simultaneous measurements of electrical resistivity and unelastic strain accumulation in Ti - 49.5 at. % Ni undergoing two-step B2→R→B19′ martensitic transformation were performed. To exclude the influence of specimen size changes during the deformation all experiments were made in torsion. It was detected that noticeable part of strain recovery after heating under a stress and active deformation in martensitic state takes place before the start of the reverse transformation and obviously is connected with twinning. At the same time the two-way shape memory effects are caused by the martensitic transformation.