Measurements have been made on single crystals of CuZn and Cu3Au held at various temperatures belowTcto decide whether there is a single‐ordered phase whose order changes with temperature, or whether there is an ordered and a disordered phase the relative amounts changing with temperature. Precision measurements were made of the position and width of the (222) CuZn and (400) Cu3Au reflections. The disordered phase has a larger cell dimension, so that reflections from the ordered and disordered phases are slightly displaced from one another. For both materials, a single peak was observed which was too narrow to correspond to the existence of two phases. At the stoichiometric compositions, it is concluded that belowTcthere is only an ordered phase whose long‐range order varies with temperature. Measurements of the long‐range order in Cu3Au have been made on briquets of filings, using quenched samples, and on a sample held at temperature.