The present paper relates theoretical assumptions concerning the pressure of oxygen required for the process of monocrystallization of the Mn,ZnbFe,O, manganese-zinc ferrites.A general analysis of the equilibrium diagram Zn-Mn-Fe-0 was carried out, taking into account the pseudobinary ZnFe,O,-MnFe,O, system for the case of the formation of the above mentioned ferrite. At the same time, it was assumed that the base material (a p l ycrystal) for the unidirectional solidification in a Bridgman system would be formed of two compounds, i.e.f ZnFe,O, and MnFe,O,.It was stated that the monocrystallization of manganese-zinc ferrites should be carried out in the working chamber of a furnace at a pressure of oxygen amounting to from several tenth t o several megapascals, the values of these pressures depending on the composition of the crystalline phase (the values of X2,&fnFepOI and Xl,Fe,O, used in Equation (12)).