Ordering and disordering treatments have been given to an alloy of composition corresponding to Cu3Au to produce a range of order and domain size values not obtainable by any other technique. Flow stresses in polycrystalline materials have been obtained for a range of grain sizes, and the results examined in terms of several previously suggested models of strengthening. While the model of Stoloff and Davies based on the transition from single dislocations to superlattice dislocations appears to be best capable of explaining the results, the agreement is little better than qualitative.