We study the influence of adding palladium or copper to the nickel sublattice or tungsten to the molybdenum sublattice on the ordering temperature, using methods of high-temperature diffractometry and differential thermal analysis (DTA). The results on the influence of the addition of transition metals (Pd, Cu, W) to Ni4Mo on the stability of the ordered D1a phase are in complete agreement with the constitution diagrams of the respective binary systems. In fact, the low stability, as well as the absence of ordering phases A4B (or those close to them in composition) in the Pd-Mo and Cu-Mo systems, provides evidence that the corresponding ordering energy is low in modulus. Of course, this lowers the thermodynamic stability of phases (Ni1-xPdx)4Mo and (Ni1-xCux)4Mo relative to binary Ni4Mo.