Invertase and gamma-Fe2O3 (8-24%) were immobilized in a copolymer gel of N-isopropylacrylamide (NIPA) and acrylamide (AAm) (NIPA/AAm gel). Sucrose hydrolysis was studied using a column packed with NIPA/AAm gel immobilized enzyme under exposure to a magnetic field (effective value 830 Oe, maximum value 1,170 Oe, 1.68-2.66 kHz). The column temperature rose from 24-25 to 31-56 degrees C due to the heat generated from magnetic hysteresis loss. When the magnetic held was applied, the overall concentration of reducing sugars In the outlet solution increased initially and then decreased due to thermal shrinkage of the gel support. This result clearly demonstrates the potential utility of the present gel-entrapment system in the magnetic control of immobilized enzyme reactions.