For monocrystalline MnZn ferrous ferrite the magnetocrystalline anisotropy constantsK1andK2, the initial permeability &mgr;i, and the saturation magnetizationMshave been measured in considerable detail as functions of temperatureT. The effect ofK2has been incorporated in the commonly used expressions describing the dependence onK1andMsof &mgr;idue to rotation of magnetization and displacement of domain walls. It is shown that a nonzeroK2can limit considerably the secondary maximum of &mgr;i(T) at the temperature of anisotropy compensation. The results of measurements on monocrystalline Mn0.42Zn0.44Fe2.145O4are interpreted with the aid of the theoretical expressions obtained for &mgr;ias a function ofK1,K2, andMs. Special attention has been paid to the temperature range around the secondary maximum of &mgr;i(T) at −82 °C and the temperature range around the primary maximum of &mgr;i(T) close to the Curie temperature.