1. In addition to the eutectic component Mg2Zn3, zirconides Zn2Zr3, ZnZr, and Zn2Zr were found in Mg\t-Zn\t-Zr alloys. 2. Mg2Zn3 goes into solution with heating of alloys containing more than 7% Zn. During subsequent aging the Mg2Zn3 and MgZn phases are precipitated. The high ultimate strength of ML 12 and ML5 alloys after treatment T6 is due to decomposition of the solid solution and precipitation of secondary dispersed Laves phase Zn2Zr. 3. Cadmium does not form intermetallic compounds in alloy VML5, but hardens the solid solution. Small additions of neodymium have a modifying effect. 4. The high concentration of hydrogen in alloy ML12 leads to the formation of primary Laves phase Zn2Zr in the grain boundaries and intergranular fracture of the alloy. Hydrogen favors the formation of primary zirconides Zn2Zr3 and ZnZr in alloy VML5, which reduces its relative elongation.