To further the study of factors affecting the formation of ternary alloys, the constitution of the system Copper-Zinc-Cadium has been examined by X-ray and micrographic methods. An isothermal section has been established at 500°C showing the presence of a ternary Laves phase Cd(CuZn)2 having the C[15] structure. A compound CdNi2 has been discovered and shown to possess the C[36] structure. Together with data on the binary Laves phase CdCu[2], these results are discussed with reference to the factors affecting the formtion of these phases. The form of the ternary system is discussed in relation to atomic size effects and compound formation on termry systems.