A dental alloy consisting of Ag-Pd-Cu-Au has been annealed at various temperatures and subsequently quenched to produce a solid solution before a hardening heat treatment. The phases present were studied by means of X-ray diffraction measurements. As in conventional Au-Ag-Cu alloys, an equilibrium of two FCC (face-centered cubic) phases existed up to the solid solution annealing temperature, which is considerably higher in the present alloy (900°C). However, even a rapid quench from 900°C caused a small amount of decomposition of the matrix. The X-ray diffractogram indicated that this new phase is CuPd with a CsCl(B2) superstructure. The greatest hardness after age-hardening at 350°C was achieved with a proper prerequisite solid-solution annealing.