12-molybdocerate(IV) gel labelled with99Mo has been prepared via isotope exchange between a column of inactive molybdate matrix and a mobile solution of99-Mo-sodium molybdate(VI) in 0.1 mol·dm–3 HNO3. The composition and nature of the reaction mixture, concentration of Mo(VI) in the reactants, reaction temperature and/or drying temperature of the gel matrix on the exchange yeild of99Mo and time of reaction are explored using the batch equilibration and/or the chromatographic column methods. The obtained material is evaluated for use in preparation of elution-type99Mo-99mTc generators.