Pressure-shear plate impact experiments have been used to study the kinetics of martensitic phase transformations in polycrystalline NiTi—a shape-memory alloy. From symmetric impact experiments the limiting shear stress at which the transformation occurs is found to be46&hthinsp;MPa.From experiments in which a thin NiTi foil is sandwiched between two hard plates, The transformation process appears to involve the propagation of a diffuse boundary, resulting in a gradual increase in the shear stress transmitted through the specimen. Full transformation of160&hthinsp;&mgr;mfoils occurs in approximately0.8&hthinsp;&mgr;sunder the impact conditions of the experiments. Time dependent Landau-Ginzburg equations are introduced to model the volume fraction transformed to each of the variants in each of the grains. Comparison of theory and experiment allows the kinetic coefficient in the equations to be determined. ©2000 American Institute of Physics.