Mercerized macroporous cellulose membranes with large pore sizes (0.5-1 mum) and high porosity (about 55%) were prepared from filter paper by mercerization (caustic treatment) followed by chemical crosslinking. These membranes were activated by introducing epoxy, aldehyde or aniline groups, before trypsin was immobilized as an affinity ligand. The activities and stabilities of the immobilized trypsin membranes prepared by several methods, in the hydrolysis of N-alpha-benzoyl-L-arginine p-nitroanilide (BAPNA), were investigated and compared. The immobilized trypsin membranes were employed to separate trypsin inhibitor from the egg white.