The transfer of the radionuclide 60Co from feed to milk, meat and the organs of a cow and its incorporation into vitamin B12 were studied in order to determine the transfer coefficient of 60Co into vitamin B12 in cattle. Upper limits of transfer coefficients for 60Co organically complexed into vitamin B12 were determined to be 6·0 × 10-5 days/litre in milk and 3·9 × 10-5 days/kg in meat, based on values measured after 140 days in bovine liver.