A polycrystalline Ni51.9Mn25.1Ga23.0 alloy was heat treated in a magnetic field. The results show that enhanced MFIS has been achieved due to some preferential orientation of twin variants in the formed martensite phase as metallographic observation revealed, even if the parent phase was not textured, e.g. by directional solidification. Slowly cooling in air through both ferromagnetic transition and martensitic transformation seems to make rather remarkable sense to the improvement than quenching or cooling from a temperature between T-e and A(f).