The pattern recognition methods and a four-parameter model, based on extended Miedema’s cellular model of alloy phases, are used to study the regularities of formation of ternary compounds between two transition elements (T, T′) and one non-transition element (N) (T-T′-N system). The criterion of formation can be expressed as some functions of ϕ (electronegativity),nws1/3 (valence electron density in Wagner-Seitz cell),R (Pauling’s metallic radii) andZ (number of valence electrons in atom).