Immobilization of protamine to the inner lumen of cellulose hollow fibers has been shown useful in preventing both heparin-and protamine-induced complications during an extracorporeal blood circulation procedure. The current study examined the effects of variables on the immobilization of protamine to cyanogen bromide (CNBr)-activated cellulose hollow fibers. The degree of protamine immobilization was controlled by three independent parameters: the amount of CNBr used during the activation process, the duration of the coupling process, and the protamine concentration in the coupling solution. By the adjustment of these parameters, cellulose fibers containing desired amounts of immobilized protamine (ranging from 1 to 20 mg of immobilized protamine per gram of dry fibers) were readily prepared.Heparin adsorption to the protamine-bound cellulose fibers was also examined. The adsorption isotherm followed a Langmuir adsorption model. The amount of heparin adsorbed was dependent on both the heparin concentration in the substrate solution and the protamine loading on the fibers. The Langmuir adsorption constant K was estimated to be 0.37 k0.06 mL/mg, whereas the saturation capacity 0, of the protamine-bound fibers increased with increasing the protamine loading.