The shock induced phase transformation in potassium chloride (from the NaCl B1 structure to the CsCl B2 structure) has been investigated using constantan strain gauges. These gauges have been mounted in pressed, polycrystalline samples in an orientation that renders them sensitive to the uniaxial strain that characterizes the plate impact geometry. At the phase transformation stress (of ∼2 GPa), measured strains of ∼ -0.1 were observed, slightly higher than the values quoted in the literature. We suggested that residual porosity within the microstructure is a possible explanation. Over impact stresses of 2.5–4.0 GPa, total measured strains agree with the work of others at the lower end of our measured range, but are significantly lower at higher stresses. We suggest that this might be due to the nonequilibrium state of the material at the time of measurement. © 2000 American Institute of Physics.