The phase equilibria of the ternary Al-AlCo-AlNi system are demonstrated using isothermal sections at 1170, 1100, 1050, 900, 850, 730, and 600 degrees C. These are based on metallographic and TEM investigations and on several temperature-concentration sections, which are investigated using thermal analyses. The Scheil reaction scheme is used for explanation of the data. Eleven phases from the binaries Al-Co and Al-Ni and the three ternary phases Y/sub 2/ (Co/sub 2/NiAl/sub 9/), X and D were found at room temperature. The binary high-temperature phase Co/sub 4/Al/sub 13/(h) is stabilized in the ternary down to room temperature by Ni addition (Y/sub 1/). The phase field of D is composed of several modifications which can hardly be distinguished by light microscopy. These modifications are not considered in the present paper. 45 three-phase regions can be derived from the reaction scheme in the Al-AlCo-AlNi subsystem.