We have used in situ x-ray diffraction to measure strain curves of single crystals of 92% Pb(Zn1/3Nb2/3)O3–8% PbTiO3 poled in the 〈001〉 direction. We observed shifts in the (002) and (330) peaks as functions of applied voltage (in the 〈001〉 direction), thereby measuring the crystallographic strain. Our measurements confirm that the high strains observed using macroscopic methods reflect microscopic strains in the crystal lattice. By watching the disappearance of a rhombohedral splitting in the (330) peak, we also find direct evidence that the field-induced phase transition reported by S.-E. Park and T. R. Shrout [J. Appl. Phys. 82, 1804 (1997)] occurs between a pseudorhombohedral and tetragonal crystal structure. © 1999 American Institute of Physics.