The magnetic susceptibility measurements were performed on CuO before and after quenching from high temperature. A large increase in the magnetic susceptibility is observed by quenching or consequent decrease in the oxygen content. It is argued that the large rise in the magnetization at temperatures much below the Néel temperature observed in certain samples may not be of impurity origin but results from the random freezing of isolated Cu2+ ions near the oxygen defects. © 1990.