The magnetization of manganese ferrite has been measured at low temperatures on samples prepared at several values of oxygen pressure and temperature within the stability field of the material. The systematic variation observed which extends from 4.55 to 4.88 Bohr magnetons is correlated with the degree of oxidation (determined by weight gain and lattice constant measurements) and possible changes occurring during quenching. Some suggestions are made concerning the wide spread in the Bohr magneton values previously reported in the literature.