Moire fringe patterns, formed in electron images of one crystal superimposed on another, have been used to determine the departure from the model for a coincidence grain boundary which assumes that the coincidence lattice is continuous across the boundary. The boundary studied was the (112) lateral twin boundary in gold. The measurements revealed that the crystals on either side of the boundary were displaced towards one another by a distance which varied greatly but whose average value was 0·056 nm. © 1977, Taylor & Francis Group, LLC. All rights reserved.