A successful procedure for attaching cellulase to 45 microm iron oxide particles with a high-molecular-weight (1000) ligand has been developed. Mass and activity balances were calculated for immobilized enzymes with different loadings. The highest specific activity of the immobilized enzyme was 5.9 mmol glucose/g bound protein/h. The efficacy of retaining enzymatic activity was 128%. The optimum pH was 5.5 compared to 4.0 of the free enzyme. The half-life of the IMC was extended to 272 h compared to 0.77 h of the free enzyme.