[en] Heterogeneous equilibria in three-component systems (Pb-Sn-Te and In-Ga-P) with continuous series of solid solutions between the binary compounds (PbTe and SnTe, and InP and GaP respectively) forming in them have been studied. Choosing a solvent for liquid-phase epitaxy it is necessary to proceed from distribution coefficients of the components, which depend on particular physico-chemical reactions in the systems, as well as from the desired composition of the solid solution. The qualitative criterion is the difference in melting points and enthalpies of formation of the compound formation