- The constitution of the Al− Pd− Pt alloy system was studied above 35 at.% Al at 700, 780, 900 and 1100° C. The experiments revealed the formation of wide extensions of the binary Al− Pd and Al− Pt phases but no ternary phases. Continuous regions are probably formed between the isostructural phases Al 4 TM, Al 21 TM 8, high-temperature AlTM, low- temperature AlTM and Al 3 TM 5 (TM= Pd or Pt). The continuity between the Al 3 TM 2 phases was revealed at 900° C, while at 1100° C the regions mutually extended from Al 3 Ni 2 and Al 3 Pd 2 are separated by the ternary extension of Al 2 Pt. The latter phase was found to dissolve up to 24 at.% Pd, which resulted in a sharp decrease of its Al concentration. The Al− Pd ε-phase was found to extend up to 18 at.% Pt at practically constant Al, while the Al− Pt ξ-phase was found to extend up to 7 at.% Pd.