The strain variation under constant tensile stress of 50 MPa during isothermal holding of the quenched Ni₅₁Ti₄₉ shape memory alloy is reported for the first time. A maximum strain of 0.4% is observed during holding at a temperature of −37 °C, which is 6 °C less than the start temperature of the martensitic transformation (M_s ^σ). A shift in the holding temperature above or below the M_s ^σ temperature decreases the isothermal strain. It is shown that the strain that appears during isothermal holding completely recovers on subsequent heating. This allows one to conclude that the strain variation on holding is caused by the martensitic transformation that occurs under isothermal conditions.